Gold from Corsair: Corsair AX PSU Series Roundup

Today we are going to talk about three power supply units from the Corsair AX 80 PLUS Gold certified series with the wattage ranging from 650 to 850 watts.

by Dmitry Vasiliev
05/17/2012 | 07:44 AM

High-efficiency PSUs are getting more and more popular these days. They are available from more brands and at more affordable prices.


Corsair is one of the PSU makers that offer PSUs with the 80 PLUS Gold certification. We already know the senior model of Corsair's Gold-certified series, AX1200, which is based on a Flextronics platform. The rest of the AX series, which is also known as Professional Series Gold, are based on Seasonic’s well-known X Gold PSUs.

Thus, Corsair’s AX650, AX750 and AX850 match Seasonic’s SS-660KM, SS-760KM and SS-850KM, respectively, in their parameters but cost considerably less. So, our goal is to make sure that Seasonic's quality is as high in the products they make for Corsair as in Seasonic's own PSUs.

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.

Closer Look at Corsair AX650, AX750 and AX850

Packaging and Accessories

The packaging of the junior models of Corsair's Gold-certified PSU series is similar in size and contents to that of Seasonic's X Gold except for its exterior design.

Corsair preferred to show the modular connectors instead of the opposite PSU panel as on Seasonic’s packaging.

On the back of the box you can find a description of the product’s key features in several languages, a list of its connectors, and tables with its electrical specs, efficiency and fan regulation algorithm.

Each model of the series comes in an individual box, although they all share the same design style.

Besides the PSU, the box contains a pouch with detachable cables, another pouch for the PSU, fasteners, a system case sticker, a few cable straps, and a user manual.

Everything seems to be the same as with Seasonic’s PSUs, but Corsair’s accessories betray some cost-cutting measures on closer inspection. The cable pouch is simpler in design. The PSU pouch is made of ordinary synthetic fabric rather than velvet. There are no reusable cable straps in the box and the user manual looks cheaper.

On the other hand, the accessories include everything you expect to find in a PSU box (and even some more). So if this difference in nuances has helped Corsair bring the price down, we don't mind it.

Exterior Design

Except for the labels, the Corsair PSUs look almost exactly like their Seasonic counterparts.

The characteristic panel with modular connectors betrays their kinship with Seasonic. Next to it, there are five vent slits, four on one side of the connectors and one on the other side. The sophisticated case design is also reminiscent of Seasonic.

The main external difference is about the cooling fan. The familiar Sanyo Denki is covered by a conventional wire grid rather than by Seasonic’s punched-out honeycomb mesh. We don’t mind this simplification because the wire grid causes less resistance to the air flow, even though doesn’t look very attractive.

There’s another simplification on the back panel. We see an ordinary sticker instead of a badge with metallized logo there.

We find no other differences from Seasonic's original products.

Circuit Design

The interior design copies Seasonic's Gold-certified series in every detail. We can see DC-DC converters on the modular connector card, modest-sized heatsinks, a lot of solid-state capacitors in the output circuitry, and a number of other familiar features like the synchronous rectifier based on field-effect transistors instead of diodes.

The only difference is merely visual: the PCBs and heatsinks of the Corsair-branded PSUs are all consistently black whereas the original Seasonics sported a number of colors.


If we take a closer look, we can see stickers with Corsair’s AX marking on a couple of daughter cards. These cards had stickers with Seasonic’s KM marking in the original PSUs, so we can expect some differences between these components. We can't be sure because we don't have the Seasonic PSUs or their photos at hand. Anyway, we'll see during our tests if there are indeed any differences showing up in practice.

Each of the three Corsair PSUs has the same interior design. They only differ in the ratings of certain components and the number of solid-state capacitors installed in the output circuit (the 650W model has four empty places for such capacitors; the 750W model has two empty places; and the highest-wattage model comes with all the capacitors installed).

Like their Seasonic counterparts, the Corsair PSUs have electrolytic capacitors from United Chemi-Con which enjoy an excellent reputation.

Cables and Connectors

The three PSUs from Corsair are all modular and come with similar sets of cables. The AX650 model comes with the following cables:

The 750 and 850-watt models add to this a third cable with four SATA power connectors and a 64cm CPU power cable with an 8-pin connector.

The selection of cables is similar to that of the original Seasonics but there are no cables with mixed PATA and SATA connectors. Perhaps the unified cables help reduce the manufacturing cost somehow. Although less versatile, the PATA and SATA cables of the Corsair PSUs can offer four connectors each as opposed to two or three connectors on the PATA/SATA power cables of the Seasonic X Gold series.

The cables are flat but rather stiff.

The connectors are not labeled on the PSU (to save on the paint?) but you won’t be able to connect anything wrong. The different types of cables vary in the number of pins. The keys won't even let you plug a small male connector into a bigger female one.

So, the cable system, like the accessories, is the same as with the Seasonic PSUs but somewhat simpler and cheaper, with less attention to the ease of connection.


As expected, the specifications are almost identical to those of the corresponding Seasonic PSUs except that the total output power of the two junior models is 10 watts lower: 650 and 750 watts instead of Seasonic's 660 and 760 watts. People at Corsair seem to be fond of round numbers. As a result, they had to lower the load capacity of the 750W model’s +12V rail by 1 ampere so that it wasn't higher than the PSU's total output power.

The rest of the electrical parameters coincide with those of Seasonic's original products and are up to today's requirements. Each PSU can deliver almost all of its power across the +12V rail. The load capacity of the +3.3V and +5V rails is rather low, yet modern systems will need no more than one third or one half of that, anyway.

And we can remind you that these PSUs comply with the 80 PLUS Gold standard.

UPS Compatibility

Working together with our APC SmartUPS SC 620, the Corsair AX650 was stable at loads up to 415 watts when powered by the mains and could switch to the UPS’s batteries at loads up to 300 watts.

The higher-wattage models could work with the same UPS at loads up to 425-428 watts but neither of them could switch to the batteries even at 280 watts.

These results are worse than those of the original Seasonics which could switch to the UPS's batteries at 320-340 watts. We don't have enough statistical data to say if it's just an accident or not.

Cross-Load Voltage Stability

The Seasonic X Gold series is, unfortunately, far from perfect in terms of output voltages. Although it meets the industry requirements, its results in this test are worse than what we can expect from PSUs with dedicated voltage regulation. In every X Gold series PSU we’ve tested so far, at least one voltage was 4% off the required level.

The Corsair PSUs turned out to be somewhat better than their Seasonic counterparts, though.

The AX650 is the best one in this test. Its voltages deflect no more than by 3%. And it is only at low overall loads that the +12V and +3.3V voltages can be more than 2% off the required levels.

The 750W Corsair is almost as good as its junior cousin, but has a larger 3% zone on the +12V rail. It keeps all of its voltages within 3% of the required levels, too.

The highest-wattage model is the worst of the three. Its voltages can get 4% off the required levels on the +12V and +5V rails. This can only occur at unrealistic loads, though. Its voltages are going to be within 3% in the typical load range.

Output Voltage Ripple

The Corsair PSUs have similar results in this test.

The highest-wattage model has the strongest high-frequency ripple, but easily meets the industry requirements anyway.

The medium model has the strongest voltage ripple at the double frequency of the mains, but meets the industry requirements, too.

These results are excellent, just as we have come to expect from Seasonic's advanced PSU platforms.

Temperature and Noise

Each Corsair PSU, like its Seasonic counterpart, is cooled by a 7-blade 120mm Sanyo Denki San Ace 120 fan (model number: 9S1212F404, rated speed: 2200 RPM). Such fans are high-quality products with individual balance correction and do not produce any unwanted sounds at work. All you can hear is the pure aerodynamic noise, irrespective of the fan’s speed.

About one fourth of the impeller is covered with a piece of transparent plastic to optimize air flows inside the PSU.

Notwithstanding the identical fans, the PSUs differ in noisiness because they differ in wattage. The speed regulation algorithm has remained the same since the Seasonic X Gold, though. The fan is mostly idle until a load of 150 watts (it may turn on and work for a while at below 400 RPM). Then, it rotates at a constant and low speed (less than 600 RPM) at loads up to 400 watts. And then it accelerates in a linear manner. The acceleration is so fast that the temperature of the PSU components lowers rather than stays at the same level.

The medium model is a perfect illustration of Seasonic’s fan regulation algorithm. The other two models have their peculiarities, though.

The highest-wattage model had its fan running at 1950 RPM by the 775-watt mark. Then the fan stopped to accelerate and the difference in temperature between the incoming and outgoing air began to increase again.

The junior model doesn’t have a long stretch of constant speed or a sudden acceleration at high loads. As a result, its fan speed at a load of 650 watts is the lowest among all the PSUs based on this platform we've tested so far: 1400 RPM instead of the usual 1500-1600 RPM.

Efficiency and Power Factor

Every PSU has a power factor of 0.98 to 0.99. That’s a high result.

The PSUs had the following efficiency at the reference loads of 20%, 50% and 100%:

Thus, every PSU proved its compliance with the 80 PLUS Gold certification (87%, 90% and 87%).

Standby Source

The PSUs are similar in this test, so we only publish the senior model’s chart. As you can see, the standby source copes with its job, its voltage always being within 3% of the required level.


According to our tests, Corsair’s Gold-certified PSUs are basically the same as the well-known Seasonic X Gold series with but a few nuances in terms of technologies and usability.

From a technical standpoint, the Corsair PSUs deliver more stable voltages, but have lower compatibility with UPSes. As for usability, they come with a less handy (but larger) selection of cables and have simpler accessories.

With differences being so few and so small, price becomes the most important factor, and the Corsair PSUs are considerably cheaper than their Seasonic X Gold counterparts. You’ve got a chance to get a high-quality PSU for less money!

We'd like to note that the 650-watt model proved to be superior to its cousins in the UPS compatibility and voltage stability tests. Its fan regulation algorithm also seems to have been improved somewhat. We don’t know if it’s just some variation in product parameters or the AX650 is indeed somewhat better than the higher-wattage models of the same series due to some optimizations. The latter version is quite plausible because the AX650 is the most recent addition to the Professional Series Gold. The user manual of our AX750 doesn’t even mention the junior model of the series.