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Corsair HX850W (CMPSU-850HX)

The HX series of Corsair power supplies is supposed to be a top series although often does not differ much from the mainstream TX. Today, I will check out the difference by testing an expensive HX850W model first and then comparing it with a TX850W.

The PSU comes in a medium-sized box. Corsair has a particular color for each series: blue for the HX, yellow for the TX and green for the inexpensive VX series.

Exterior Design

The same blue color is used in the design of the PSU itself. Every label is blue. Otherwise, it is an ordinary box painted a matte black paint.

Like most PSUs of its class, the HX850W is modular. It has six connectors for peripheral power cables and four for graphics cards. The connectors differ from each other in their color and number of pins, so you can hardly confuse them.

Interior Design

The Corsair HX series is associated with Seasonic by many users. It is by Seasonic that the expensive but popular HX520W and HX620W were manufactured. However, the HX850W (and the higher-wattage HX1000W) is produced by another renowned maker, Channel Well Technology (CWT).

This model has nothing in common with the HX1000W which had a very queer design (in fact, it consisted of two 500-watt power supplies in a single housing). It is not the well-known PSH platform Channel Well has been using for years to produce PSUs for many brands, either.

The main distinguishing feature of the new platform is the use of two DC-DC converters to obtain +3.3 and +5 V. In other words, the main part of the power supply generates +12 V whereas the lower voltages are produced out of +12 V by means of full-featured converters (as opposed to PSUs with regulators based on magnetic amplifiers which are not truly independent and can only work when driven by a switching voltage). You can see the two DC-DC cards in the photo above.

This design ensures good voltage stability (I will check this out shortly) as well as higher component density (the upright converter cards take rather little space). It also makes the main power transformer simpler as the latter now has only one secondary winding for +12 V and no 5V tap. Until recently, such converters have been rare due to high cost, but seem to be ready now to become a de facto standard for mainstream and top-end PSUs, replacing magnetic regulators with their bulky chokes.

The PSU has both solid-state capacitors (in the DC-DC converters) and electrolytic ones (KZE series from United Chemi-Con) at the output.


This PSU has a solid +12V power rail without any “virtual” output lines. The max load on that rail is a mere 10 watts lower than the total allowable load for this PSU. The HX850 is ideal in this respect.

Cables and Connectors

The PSU is equipped with the following cables and connectors:

  • Mainboard cable with a 20+4-pin connector (58 cm)
  • One CPU cable with a 4+4-pin connector (60 cm)
  • Two graphics card cables with one 6+2-pin connector on each (60 cm)
  • Four connectors for graphics card cables
  • Six connectors for peripheral power cables

Included with the PSU are:

  • Four graphics card cables with one 6+2-pin connector on each (60 cm)
  • Three cables with four PATA power connectors on each (40+14+14+14 cm)
  • Three cables with four SATA power connectors on each (40+14+14+14 cm)
  • Two adapters from PATA power connectors to floppy-drive plugs

There are as many as six graphics card cables here! The PSU can power up to three top-end graphics cards with 8-pin power connectors without any adapters. Most 850W units offer but four connectors, so if you are going to assemble a 3-way GPU configuration, you may consider the Corsair HX850W as an option.

UPS Compatibility

Working with my APC SmartUPS SC 620, this power supply was stable at loads up to 372 watts when powered by the mains and up to 350 watts when powered by the batteries. They had no problems switching to the UPS’s batteries.

Output Voltage Stability



The PSU keeps its output voltages very stable: the +12V voltage barely goes beyond 1% deflection. The +5V is within 2% and the +3.3V voltage is within 3% from the nominal value.

Output Voltage Ripple



High-frequency voltage ripple can hardly be observed at the output of the HX850W even at full load. The oscillogram shows but small spikes of voltage which are far below the permissible limits.


This PSU is cooled by a 140x140x25mm fan from Yate Loon. Its impeller is partially covered by an intricately shaped plate that helps avoid a dead zone at the back of the PSU case in which the speed of the airflow would be too low to cool the components effectively.

The fan starts out at 1000 RPM and keeps this speed until a load of 600 watts. At full load the fan is barely faster than 1350 RPM.

The PSU cannot be called silent due to the rather high initial speed of the fan, but under high loads it proves to be quieter than most opponents which accelerate their fans in a more aggressive way. Thus, the noisiness of the HX850W is going to depend on how advanced and hot your particular configuration is.

Efficiency and Power Factor


Not long ago I used to be very glad to see PSUs with an efficiency of 80% and higher. But now we’ve got models that are over 90% efficient! The efficiency lowers only to 89% at full load, which is an excellent result.

Standby Source


The output voltage of the standby source lowers by a mere 0.1 V as the load changes from zero to maximum. It remains much higher than the permissible bottom limit.


The Corsair HX850W has no serious drawbacks. Its voltages are stable and there is low output voltage ripple. It is highly efficient and offers a lot of connectors with which you can connect three graphics cards and about ten hard disk drives using no adapters. The only thing I can find fault with is that the fan is never slower than 1000 RPM. It means you should not buy the HX850W for a mainstream PC configuration, hoping that it will be silent. On the other hand, this PSU is going to be an excellent choice for high-performance computers.

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