Corsair CX400W Power Supply

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Dec 15, 2009 by Mike Vass

Corsair Power 400W (CMPSU-400CX) Computer Power Supply
Market Price
US$50 - $65

Corsair has been offering power supply units, based on Seasonic and Channel Well platforms, for the past three or so years. SPCR reviewed a handful of them — the VX450W, TX650W, and both the HX520W and HX620W — and reported consistently excellent performance. Naturally, the lineup has expanded, mostly upwards to the kilowatt level... but the CX400W is a counterpoint to the rest of the Corsair power line, with just 400W maximum power at a very modest price. As you might expect, Corsair claims the CX400W makes no sacrifices on performance.

A 400W-rated PSU is generally seen today as a "low-end" model, though we've seen in the past that many very capable systems don't draw more anywhere close to 400W. It's the inclusion of high end gaming cards, particularly two or more such cards, that makes the power demand jump. Some manufacturer rebates have pulled the price of the CX400W under $50 this holiday season, so it really does compete in the lowest price category of power supply units.

Like the VX450W and TX650W, but unlike the HX520W and HX620W, the power cables on the CX400W are permanently attached. This is expected for such a low cost model, and has the theoretical advantage of reducing overall voltage drops through the cabling.


The box features minimalistic artwork, with less focus on feature listings compared to previous Corsair models.

Corsair CX400W FEATURE HIGHLIGHTS (from the web product page)
Features Our comment
Supports the latest ATX12V v2.2 standard and is backwards compatible with ATX12V 2.01 systems. Good to see.
Rated up to 400W of continuous power output at 40ºC
Notice the 40ºC: A realistic operating temperature.
Extra long fully sleeved cables to support full tower chassis and assist with flexible cable routing. In leiu of modular cables, this is a nice feature to have.
Ultra-quiet 120mm double ball-bearing fan delivers excellent airflow at an exceptionally low noise level by varying the RPM in response to temperature.

Of course, the airflow has to turn 90º to exhaust, but this is pretty typical. Hopefully the fan is indeed "ultra-quiet"

High efficiency topology to ensure energy savings.

The CX400W is branded basic 80Plus, so expect good efficiency, not stellar efficiency.

99% Active Power Factor Correction provides clean and reliable power to your system. This is important if you buy by the Volt-Ampere, rather than the Watt.
Universal AC input 90~264V automatically scans and detects the correct voltage. No more hassle of flipping that red switch! Nice to know about the switch. Notice the 90V lower limit. This is very good.
Dedicated single +12V rail offers maximum compatibility with latest components The honesty about a shared 12V line is nice!
Over Current/Voltage/Power Protection, Under Voltage Protection, and Short Circuit Protection provide maximum safety to your critical system components. OK.
Standard ATX PS/2 size: 5.9"(W) x 3.4"(H) X 5.5"(L); 150mm(W) x 86mm(H) x 140mm(L) Yep, this is pretty standard.
MTBF: 100,000 Hours 11.4 Years. I like the optimism!


Power specifications are shown on a convenient sticker right on the top of the unit:

Corsair CMPSU-400CX (CX400W) Specifications
AC Input
100-240V - 7A 50/60Hz (Differs from website)
DC Output

Strangely, the AC Input specifications vary with respect to the website's specs for the same supply: 100-240V - 7A - 50/60Hz written on the label, versus 90-264V - 5-9A - 47-63Hz on the website. That 10VAC on the lower end could make a difference in brownout conditions.

Our sample lacked any 80 Plus labelling, but it is clearly among Corsair passed models listed at the 80 Plus web site. Keep in mind that the testing for 80 Plus approval is done at normal ambient room temperature. The 80 Plus Testing Guidelines (PDF) specify only that "ambient temperature shall be maintained at 23°C ± 5°C throughout the test." In contrast, the ambient temperature of the SPCR test system is directly proportionate to the load. At low load, the air intake is at or just above room temperature, but as load is increased, the temperature rises steadily. Typically, with a fan-cooled PSU, the intake temperature in our test system reaches 45~50¬įC at >600W loads. This is an extremely tough test condition, as PSU efficiency naturally drops off at high and low loads; combine high load with high temperature and it's essentially a torture chamber. It does replicate reasonably well the conditions that prevail in a typical tower PC. For full details, please refer to SPCR's PSU Test Platform V4.1.

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