Gold for Everyone: Power Supply Unit Roundup

Today we are going to talk about five power supply units from Cooler Master, Cougar, OCZ and Seasonic certified according to 80 PLUS Gold standard. Their wattage ranges from 600 to 1050 W, which provides a choice to everyone who is looking for a quality PSU.

by Dmitry Vasiliev
03/19/2012 | 03:30 AM

Power supply units for personal computers have recently been evolving in two ways. First of all, they have been progressing in terms of efficiency and wattage. And second, technologically advanced solutions have become more affordable. When the FSP Epsilon series was released back in 2006, the 700-watt model cost almost $200 and that was considered quite a normal price for such an efficient and high-wattage PSU. Today, you can spend the same money and have a PSU with 50% more wattage and much higher efficiency whereas the current generation of Epsilon PSUs costs only half as much, the wattage being the same.

 

It is no wonder then that users are increasingly more interested in high-efficiency solutions. An efficient PSU not only contributes to saving our planet’s resources and cutting your electricity bill but has a better chance of being quiet. Higher efficiency means that less power is dissipated as useless heat. And less heat means that the PSU’s cooling fan can work at a lower speed and be quieter.

So, today we are going to discuss as many as five PSUs that are certified to comply with the 80 PLUS Gold standard. Four of them (the two Cougars and the products from Cooler Master and OCZ) come from the mentioned category of affordable but very efficient products (the 1-kilowatt models are available for about $200 whereas the lower-wattage ones are even cheaper).

We’ll also take Seasonic’s X-850 (SS-850KM) as a kind of a reference point. It is an 80 PLUS Gold product that comes from the famous X-Gold series whose junior models have already been tested in our labs before.

Let’s see if the inexpensive Gold-certified PSUs can match the recognized market leader.

Testing Methodology

The following article offers a detailed description of our testing methodology and equipment and a brief explanation of what the specified and tested parameters of power supplies mean: X-bit Labs Presents: Power Supply Units Testing Methodology. If you feel overwhelmed with the numbers and terms this review abounds in, refer to the Methodology.

You can also go to our Cases/PSU section to check out reviews of all other PSU models we have tested in our labs.

We will mark the actual power consumption of three system configurations (discussed in our article PC Power Consumption: How Many Watts Do We Need?) in the cross-load diagrams. This will help you see if the tested PSU can meet the requirements of a real-life PC.

Testing Participants

Cooler Master Silent Pro Gold 600W

We were not at all impressed with the Cooler Master PSUs we tested in our recent roundup but those were cheaper products. The Gold-certified model is different, its higher status evident even in its packaging.

The Silent Pro Gold comes in a large black-and-gold box that lacks a carry handle.

Product features and electrical parameters are listed on the back of the box. By the way, each model in the Silent Pro Gold series, which ranges from 600 to 1200 watts, has individual packaging.

Besides the PSU, the box contains a mains cord, fasteners, a neat envelope with a user manual and warranty card, and a cute pouch for detachable cables. Everything is designed in a consistent black-and-gold style.

Exterior Design

The PSU itself follows the overall design concept. It’s got a black case with some elements that try hard, perhaps not very successfully, to look golden.

The back panel is mostly a large honeycomb vent grid embellished with a Cooler Master logo.

The Silent Pro Gold features modular design. Its power cables are all detachable, except for the indispensable mainboard and CPU ones.

There are no additional vent holes in the PSU case.

Circuit Design

The familiar shape of the fingered heatsinks makes it easy to identify the real maker of this PSU. Like the lackluster Cooler Master GX 750W, this product is based on an Enhance platform.

It boasts every accomplishment of a top-class PSU: dedicated voltage regulation based on DC-DC converters, active power factor correction, and multistep output voltage filtering.

The daughter cards with DC-DC converters are placed crosswise between the output circuitry and the mains connector.

The voltage converters are based on a PWM controller APW7073 which also protects the PSUs against overvoltage and undervoltage.

You can see smoothing capacitors on the card with the connectors for modular cables. There are high-quality electrolytic capacitors from United Chemi-Con’s KY and KZE series at the PSU’s output.

Cables and Connectors

The Silent Pro Gold 600W has the following cables and connectors:

Included with the PSU are:

Perhaps the connectors are placed too close to each other on the detachable cables, but the latter are flexible enough to make up for this shortcoming. When an ordinary cable would be too stiff to take the required shape, a Cooler Master cable can do the job easily.

Specifications

The product specifications are up to today’s requirements, too. The Silent Pro Gold 600W can provide up to 576 out of its total 600 watts via the +12V rail.

The +12V voltage is implemented as a single power rail, so you don’t have to worry about overloading a particular “virtual” output line of a modest load capacity.

The combined load capacity of the +3.3 and +5V rails is expectedly very high. The PSU can deliver up to 150 watts (up to 25 amperes per each) across them, although today’s computers rarely need more than 50 watts.

UPS Compatibility

Connected to our APC SmartUPS SC 620, this PSU was stable at loads up to 410 watts when powered by the mains but could only switch to the UPS’s batteries at a load of 280 watts.

Cross-Load Voltage Stability

The +12 and +5V voltages are almost ideal, keeping within 2% from the required levels.

The +3.3V rail is but slightly worse. It deflects by 3% from the required level at low loads.

So, the Silent Pro Gold 600W can deliver very stable voltages to your components.

Output Voltage Ripple

The high-frequency ripple is rather strong but fits within the industry requirements.

The same goes for the low-frequency ripple (at the double frequency of the power mains).

The Silent Pro Gold 600W passes this test but by a very small margin.

Temperature and Noise

The Silent Pro Gold 600W is cooled by a 7-blade 120mm fan from Young Lin Tech (the DFB122512M model with a rated speed of 2000 RPM).

The cooling fan starts out at about 850 RPM and keeps the same speed until a load of 400 watts. After that, the speed rises up quickly, yet the top limit is not very high at 1350 RPM.

Thus, the PSU is quiet, especially as its fan didn’t produce any unwanted sounds except for the pure aerodynamic noise.

Efficiency and Power Factor

The power factor is considerably lower than usual for a PSU with active power factor correction, fluctuating between 94 and 96% throughout a larger part of the load range. This parameter isn’t critical for home users, however. Not until household electric meters begin to measure your reactive power consumption.

As for efficiency, the Silent Pro Gold 600W meets the Gold standard indeed. It is 88.2, 91.8 and 90% efficient at the three reference loads (20%, 50% and 100% of its max output power). Its peak efficiency was right at the load of 50%. Take note that the PSU remains at least 90% efficient at any loads starting from 200 watts and above.

Standby Source

The standby source easily copes with the load of 3.5 amperes, which is rather high for this power line. The voltage deflects no more than by 2% from the nominal value.

Summary

The Cooler Master Silent Pro Gold 600W has no critical downsides but does have a few advantages over same-class opponents. Its output voltages are very stable and it is very efficient at modest noise. Most importantly, this series is priced very affordably. In fact, it is comparable to Bronze-certified competitors of the same wattage that come under recognized brands like Corsair. Even the affordable Gold-certified products from Cougar can’t match Cooler Master’s offer in terms of pricing.

Cougar GX G900 and Cougar GX G1050

We’ve recently tested one Cougar, the retail brand of HEC/Compucase Group. With a higher wattage rating, that model was only compliant with the 80 PLUS Bronze standard.

The packaging of the GX series models is designed in the same style with but minor discrepancies.

Below the cover, the box is divided into four compartments: for the PSU, fixed cables, modular cables and accessories (fasteners, mains cord, a user manual and cable straps).

Exterior Design

The Cougar GX series look similar to the abovementioned CMX 1200 model.

The only difference is about the color scheme. Instead of the daring mix of red and black for the CMX series, the Gold-certified GX series is painted a calmer combination of black and gold.

You can learn the name and wattage of the particular model easily as they are indicated on the case with shiny letters.

Circuit Design

Besides looking similar to the CMX model, the GX series are alike to it inside. The component layout of the Gold-certified units is identical to that of the Bronze model except for the heatsinks, which are unusually large for such high-efficiency PSUs and have obviously been borrowed from the lower-efficiency predecessor.

The Cougar GX series features dedicated voltage regulation based on DC-DC converters, active PFC and dual-transformer design.

We could only find one difference from the Bronze-certified Cougar. The Gold-certified GX series have a lot of solid-state capacitors in the output circuitry whereas their less efficient cousin mostly employs electrolytic capacitors.

The direct current converters can also be seen here as two small upright cards. They differ from each other in their PCB design and component layout. It’s unusual as most of PSUs we’ve tested so far had identical converters for both +5V and +3.3V voltage.

Smoothing chokes and solid-state capacitors can be found on the reverse side of the converter cards.

The brands of the electrolytic capacitors haven’t changed since the CMX series: Panasonic at the input and Teapo at the output. Every capacitor is rated for an operating temperature of 105°C.

Cables and Connectors

The Cougar GX G900 model has the following cables and connectors:

Included with the PSU are:

The higher-wattage model has 6+2-pin rather than 6-pin connectors on the graphics card cables and adds a fifth SATA connector to the single SATA-only power cable.

Overall, we’ve got a sufficient number of cables and connectors here but the CPU power cable doesn’t make sense. It’s unclear why anyone would ever need a CPU cable with a total length of over 120 centimeters and two extra connectors (the 8-pin and the 4-pin ones) which are duplicated by the third 4+4-pin connector. A single 4+4-pin connector on a 70cm cable would be just fine.

Specifications

The two models are similar in their specifications. They only differ in the load capacity of the +12V rail and the combined load on the +3.3V and +5V rails (but the peak current on each of these rails is the same with both PSU models).

The load capacity of the +12V rail is close to the full output power of each PSU. The small difference is going to be easily accounted for by the other power rails.

Each of these Cougar PSUs has six “virtual” +12V lines with a max load of 25 amperes. Of course, a single high-capacity line is more flexible and easier to deal with, but the potential downsides of the implemented design are minimized here because the virtual lines are so many.

UPS Compatibility

Connected to our APC SmartUPS SC 620, the Cougar GX G900 was stable at loads up to 375 watts and the GX G1050, up to 382 watts, when powered by the mains. Both units could switch to the UPS’s batteries at loads up to 295 watts.

Cross-Load Voltage Stability

The junior model is very stable in terms of the main +12V voltage which stays within 2% of the required level at most loads and never deflects by more than 3%. The other voltages are not that stable, though.

The +5V voltage deviates as far as the maximum permissible level and beyond at near-maximum loads. It is 4% off the required level in the typical load range when there’s a high load on the +12V rail.

The +3.3V voltage never leaves the permissible range but it’s 3% off the necessary value when there is either a high load on the +12V rail or very low loads on all the rails.

The cross-load diagram of the 1050W model looks almost the same.

So, the Cougar PSUs do more or less well in this test, yet we guess that we could expect a Gold-certified PSU to be more than just satisfactory in terms of the stability of its output voltages.

Output Voltage Ripple

The two Cougar PSUs turned out to be very similar to each other in this test, so we will only show you the results of the higher-wattage model.

The high-frequency voltage ripple is within the norm, especially on the +12V rail, although the latter is permitted to have a voltage ripple of 120 millivolts as opposed to 50 millivolts on the other two rails.

It’s somewhat different at the double mains frequency: the voltage ripple on the +12V rail is stronger whereas on the +3.3V rail, weaker. Again, there are no voltage spikes shooting over the permissible limits.

Temperature and Noise

The two Cougar PSUs differ slightly in terms of cooling.

The junior model is cooled by a 140mm 7-blade Power Logic fan (it is the PLA14025S12M model with a rated speed of 1500 RPM).

The fan is almost identical to the one in the CMX 1200 model with its square impeller blades you don’t often see in other fans. The speed rating is the only difference. Thanks to the higher efficiency of the GX series, the cooling fan can be slower and has a speed rating of M (medium) instead of H (high).

The senior model’s fan looks dramatically different. It has an intricately shaped frame, two extra blades, and a different shape of the impeller with fancy grooves. Oddly enough, it has the same marking “PLA14025S12M”.

Notwithstanding their external differences, the two fans turned out to be very similar in behavior. Their speed regulation works in the same way and they seemed to be identical in terms of acoustic comfort. That’s why we only show you the speed and temperature diagram for the senior model only.

Each fan starts out at a rather low speed of 750 RPM. And in each PSU the fan keeps its initial speed until a load of 600 watts and smoothly accelerates thereafter. The fan of the senior PSU model has a top speed of about 1400 RPM whereas the junior model’s fan accelerates to about 1250 RPM. The fans rattle a little when working, but you can only hear this from a short distance. There is normally no discomfort from those sounds.

Considering their high wattage, the Cougar PSUs can be called rather quiet. They are but slightly louder at full load than the lower-wattage Cooler Master we’ve discussed above.

The low noise level comes at the expense of temperature. The difference in temperature between the incoming and outgoing air is the largest among all the PSUs in this review. That’s the consequence of the high wattage, slow cooling fan and low (for this product class) efficiency.

Efficiency and Power Factor

The two PSUs are similar to each other in this test, too, so we only publish the diagram of the higher-wattage model.

The power factor is typical of a PSU with active power factor correction, reaching 99.6% at high loads.

As for efficiency, the Cougars do not impress. They barely meet the 80 PLUS Gold requirements at the half and full output power. Considering that according to the certification guidelines the efficiency must be measured with 115V mains, which would lead to a lower efficiency than with our 230V mains, there is no reserve of efficiency at all. Neither model could notch 91% efficiency at any load.

Thus, the Cougar PSUs meet the 80 PLUS Gold requirements but do not add anything to them.

Standby Source

The two Cougar PSUs are similar in this test, too. They can easily deliver 4 amperes over the standby line.

Summary

The Gold series from Cougar is quiet at any load, up to the maximum one, has low voltage ripple and comes at a modest price compared to similar PSUs.

The downside is that their efficiency is not any better than the basic 80 PLUS Gold requirements while their +3.3 and +5V voltages are not very stable in the cross-load test.

OCZ ZX 1000W

Many companies have changed their product series over time and OCZ is no exception. Its brand used to be associated with enthusiast-targeted memory modules but now OCZ is closely associated with solid state drives. Power supply units are yet another field where the company is active.

Today we are going to take a look at OCZ’s highest-wattage product called ZX 1000W. Like the rest of the PSUs in this review, it is 80 PLUS Gold certified and only inferior to the senior Cougar in its wattage rating.

The Gold certification is confirmed not only by a logo on the PSU itself but also by the printed-out 80 PLUS Gold certificate.

Exterior Design

The exterior design of this OCZ product seems to be the most trivial among all the PSUs included into this review. It lacks the originality of the Cougar and Seasonic products and the eye-catching coloring of the Cooler Master.

It’s just a regular PSU with no distinguishing features. A big black fan peeps out of the black grid that covers the hole in the black case.

The absolute blackness is only relieved by the white spot of the label with electrical specifications and the white-and-yellow sides of the case.

Circuit Design

The hardware platform of the ZX 1000W is made by a manufacturer whose product we have not yet tested in our labs. Although the UL certificate number on the PSU label points at OCZ, the characteristic interior design and power rating help us identify the real maker as the Chinese Great Wall Company (do not confuse it with the namesake car manufacturer). This hardware platform is also used for Gold-certified PSUs selling under the Sparkle brand but, unlike the OCZ model, they are not all-modular and have fixed main cables.

The ZX 1000W has all the features you expect to find in a Gold-certified PSU: DC-DC converters for +3.3V and +5V voltages, an active PFC choke, and a card with connectors for modular cables with a lot of smoothing capacitors.

As opposed to the Cougar PSUs, the two DC-DC converters are identical in design.

Like in most high-efficiency PSUs, the heatsinks are rather small. Only one out of the two heatsinks has something like fins.

There is a PFC & PWM controller CM6802TAHX on the daughter card in the center of the PSU case.

The assembly quality is very high, just like with the rest of the PSUs in this review.

The PSU has Teapo capacitors rated for an operating temperature up to 105°C both at its input and output.

Cables and Connectors

The OCZ ZX 1000W is all modular. It has not a single fixed cable. It offers the following connectors for detachable cables:

Included with the PSU are:

You can note that there are as many as seven power cables for the PSU’s five peripheral connectors: four with SATA and three with PATA connectors. This gives you more flexibility in configuring your system and choosing what cables are needed for it. You can use more SATA power cables for an advanced disk array or PATA ones for a large number of system fans.

The PSU lacks a floppy-drive connector (or an appropriate adapter). Yes, floppy drives are absolutely outdated already, but there are other devices that connect to the PSU in this way, for example the 5.25-inch I/O module of PCI-interfaced Creative X-Fi sound cards.

Specifications

The auxiliary voltages (-12V and standby) are rather unusually combined with the +12V rail in the specifications, but there are no surprises otherwise. Like any other modern PSU, the OCZ ZX 1000W offers one high-capacity +12V rail and can deliver almost all of its full output power across it.

There is a substantial reserve of power on the +3.3V and +5V rails. Each has a load capacity of 30 amperes. Their combined load can be as high as 170 watts but no modern PC will ever need that much power from these two rails.

UPS Compatibility

Working with our APC SmartUPS SC 620, this power supply was stable at loads up to 383 watts when powered from the mains and could switch to the UPS’s batteries at loads up to 280 watts.

Cross-Load Voltage Stability

The most important +12V rail is not very stable in this test. Its voltage is 2 to 3% off the required level at loads up to 300 watts. The result is good but the other PSUs in this review are better in this respect.

You can note, however, that the +12V voltage gets more stable at higher loads, so you shouldn't worry that your top-end graphics card might fail due to poor power supply when running a heavy 3D game (such problems can occur even if the voltage is no more than 5% off as permitted by the industry standard).

The rest of the voltages are blameless, staying within 2% of the required levels.

Thus, the OCZ ZX 1000W would be perfect if it were not for the large 3% zone in the +12V diagram.

Well, this is not a critical downside, of course. We wouldn’t even notice it in a cheaper and less efficient product or on a less loaded power rail. But the OCZ ZX 1000W being a rather expensive, high-wattage and high-efficiency PSU, we want it to be more stable in terms of the +12V voltage.

Output Voltage Ripple

The high-frequency output voltage ripple is very weak on the +12V rail and two or three times lower than the permissible maximums on the other power rails.

We’ve got the same picture at the double frequency of the mains.

Temperature and Noise

The OCZ ZX 1000W is cooled by a 140mm 7-blade Yate Loon fan. It is the D14BH-12 model with a rated speed of 2800 RPM.

The fan starts out at a speed of 900 RPM and keeps it until a load of 300 watts. It accelerates then but, despite the high rated speed, gets only as fast as 1700 RPM at full load.

On the other hand, accelerating at a rather low load and having a top speed of 1700 RPM, the fan turns out to be the noisiest among the cooling fans of all the PSUs in this review. Like the above-discussed Cougars, the fan of the OCZ ZX 1000W produced some mechanical sounds besides pure aerodynamic noise.

Efficiency and Power Factor

The power factor is high, just as you can expect from a PSU with active power factor correction.

At the three reference loads (20%, 50% and 100% of the full output power), the PSU was 88.3%, 90.9% and 88.4% efficient. Its peak efficiency of 91.5% was achieved at a load of 423 watts.

These numbers are not as impressive as those of the lower-wattage models from Cooler Master and Seasonic, but better than the results of the Cougar PSUs which are similar in wattage. As opposed to the latter, the OCZ ZX 1000W is somewhat better than the basic requirements of the 80 PLUS Gold certification.

Standby Source

The standby source copes with its job, keeping its voltage within 2% of the required level.

Summary

The closest opponent to the OCZ ZX 1000W is the Cougar GX G1050. While being very close to each other in terms of their retail price and wattage, their operating parameters differ greatly.

The OCZ is superior across nearly all of electrical parameters and also features all-modular design. However, it is inferior to its opponent in acoustic comfort and UPS compatibility. Its exterior design, if you care about this factor, is less attractive, too. It's up to you to choose what parameters are more important to you.

Seasonic SS-850KM Active PFC F3

We have already tested Gold-certified products from Seasonic: SS-560KM, SS-660KM and SS-760KM. The SS-850KM is in fact the last model in this series. Although Seasonic also offers 80 PLUS Gold compliant PSUs with wattage ratings of 1050 and 1250 watts, they belong to the XM rather than KM subseries and have larger dimensions.

Since we are already familiar with products based on the same hardware platform, we won't dwell upon the SS-850KM's interior design and accessories, which are in fact identical to those of its series mates, but will instead focus on our tests.

 

  

Exterior Design

The SS-850KM is no different from the other models in the series. It features all-modular design, a sophisticated case with lots of details and mounting elements, and matte black paint.

Like the rest of the same series, the single decorative element of the SS-850KM is the Seasonic logo on the back panel which can be seen even when the PSU is installed into a system case.

Circuit Design

As for the interior design, this 850-watt model differs from the other in the same series in such nuances like a larger number of capacitors.

We don’t see any other changes here. Like the other KM series models, the Seasonic SS-850KM has DC-DC converters for +3.3 and +5V voltages on the card with connectors for modular cables. There is a single large heatsink near the side panel and a few small fingered heatsinks on the output rectifiers.

The SS-850KM employs United Chemi-Con capacitors rated for an operating temperature of 105°C.

Cables and Connectors

The Seasonic SS-850KM comes with the following power cables:

The cables are identical to those of the 760W model from the same series. We can't find any fault with them.

Specifications

When it comes to electrical specs, the SS-850KM differs from the other models in its series in the higher capacity of its +12V power rail which can deliver up to 840 out of its full 850 watts.

The combined load capacity of the +3.3 and +5V rails is lower compared to the other PSUs in this review. On the other hand, 125 watts is about twice as much as the majority of modern computers will ever need from these two power lines.

UPS Compatibility

Connected to our APC SmartUPS SC 620, the Seasonic SS-850KM was stable at loads up to 435 watts when powered by the mains. This seems to be the highest result we’ve ever observed in our PSU tests. They could switch to the UPS’s batteries at loads up to 320 watts, which is not a record, yet the best result in this review anyway.

Cross-Load Voltage Stability

We’ve been disappointed with the +12V stability of the above-discussed OCZ ZX 1000W, but the Seasonic SS-850KM is even worse in this respect. The +12V voltage gets 4% off the required level. About half of all permissible loads (including our three reference configurations) are within the 3% zone.

The +3.3V voltage is more stable, deflecting by more than 2% only when there’s very low load on all of the power rails.

The +5V rail is in fact blameless. At load distributions typical of real-life computers, this voltage is only 1% off the required level when there is near-maximum load on the +12V rail.

But if we consider all the voltages, the Seasonic SS-850KM turns out to produce the worst result in this test among all the PSUs in this review. The reason is the poor stability of the most demanded +12V voltage. The better stability of the other rails can’t save the day for this PSU.

By the way, we do not think that this performance is an accident because we’ve seen a similar picture with the earlier-tested 660W and 760W products from the same series. This is a shame especially as the user manual claims that these PSUs are going to keep their output voltages within 3% of the required levels on every power rail.

Output Voltage Ripple

Seasonic’s top-end PSUs are blameless in terms of the output voltage ripple. The high-frequency ripple is very weak on each power rail.

The graphs are almost flat lines at the double frequency of the mains, too.

Temperature and Noise

Like the other products of this series, the Seasonic SS-850KM is cooled by a 7-blade 120mm fan Sanyo Denki San Ace 120 (the 9S1212F404 model with a rated speed of 2200 RPM). Such fans are very high-quality things, up to individual impeller calibration, and produce no unwanted sounds at work. All you can hear at any speed is pure aerodynamic noise.

The fan mostly remains idle at low loads, turning on at minimum speed for brief periods of time. It switches to constant operation at a load of 150 watts but works at a very low speed (from 300 to 550 RPM), so there is no discomfort for the user. The speed remains low until a load of 600 watts but then rises up rapidly. The fan becomes audible at a load of 700 watts. Reaching a speed of 1700 RPM at full load, the fan is still comfortable enough, thanks to its high quality.

However, you can see from the diagram that there is no need for such a rapid increase in speed at high loads. The fan accelerates so fast that the difference in temperature between the incoming and outgoing air shrinks. If the speed increased at a slower rate, just enough to keep the temperature at the same level, the Seasonic SS-850KM would probably be a record-breaking PSU in terms of acoustic comfort.

As it is now, the SS-850KM is similar to the Cougar PSUs in terms of maximum noise. The latter have a lower fan speed at high loads, but the Seasonic’s fan is somewhat smaller and doesn’t rattle.

Efficiency and Power Factor

The power factor of the Seasonic SS-850KM is almost as high as 99% at high loads.

The PSU was 90%, 92.6% and 89.5% efficient at the three reference loads of 20%, 50% and 100%. Its peak efficiency was achieved at 50% load. We can also add that it is 90% or more efficient in the load range of 160 to 780 watts.

Standby Source

The standby source does its job without any problems.

Summary

There are three problems we can find about the Seasonic SS-850KM. It is expensive, its fan accelerates too rapidly at high loads, and its +12V voltage is not very stable. If it were not for the last downside, the first one might be ignored because the competitors are obviously inferior across most parameters. As for the fan, PSUs do not often work at their full capacity in real-life computers, especially as most users prefer to buy PSUs with some reserve of wattage. It means that you are unlikely to hear the full sound of this PSU’s cooling fan in real usage scenarios.

Conclusion

If you are looking for an efficient power supply with moderate wattage (within 600 W), then there are two choices among the tested models: Seasonic X-560 (SS-560KM) and Cooler Master Silent Pro Gold 600W, we haven’t tested any other PSUs with similar characteristics yet. The Seasonic is better in acoustic comfort, efficiency and output voltage ripple but the Cooler Master is cheaper while being not very inferior to its opponent in electrical parameters.

As for the other products we’ve just reviewed, the PSUs from Cougar and OCZ are comparable in price, the OCZ being slightly more expensive, but offer different sets of advantages. The OCZ ZX 1000W is better electrically (cross-load stability, efficiency, voltage ripple) than the Cougar GX series but the latter are quieter at medium and high loads, have better compatibility with UPSes and feature an eye-catching exterior.

The 850-watt Gold-certified model from Seasonic stands out among the rest. It is considerably more expensive than the other products reviewed here, although its wattage is lower than that of the Cougar and OCZ products. This implies superior characteristics, yet we don’t find them in practice. The Seasonic SS-850KM is let down by its not-very-stable +12V voltage as well as by the unjustifiably aggressive behavior of its cooling fan at high loads. Although these downsides are not critical, you may want to think twice before paying extra for this PSU. When you pay more, you want to have nothing but advantages for your money, yet the Seasonic SS-850KM can only offer you a different combination of highs and lows in comparison with the other products.