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Corsair CS850M 850W Power Supply Review

Load Regulation, Hold-Up Time And Inrush Current

To read about our PSU tests in-depth, please check out How We Test Power Supply Units.

Primary Rails And 5VSB Load Regulation

The following charts show the voltage values of the main rails, recorded over a range from 40W to the maximum specified load, and the deviation (in percent) for the same load range. You will also find a chart showing how the 5VSB rail deals with the load we throw at it.

Load Regulation testing is detailed here.

Hold-Up Time

Our hold-up time tests are described in detail here.

In this screenshot, the blue line is the mains signal and the yellow line is the “Power Good” signal. The hold-up time that our equipment measured is lower than the minimum allowed, so the PSU fails the test. Corsair should use larger APFC capacitors to achieve over 16ms hold-up time. They're not cheap though, and they have a negative effect on efficiency.

Inrush Current

For details on our inrush current testing, please click here.

Although Corsair went with smaller capacitors in the APFC converter, the registered inrush current of 230VAC is pretty high. This indicates that a larger NTC thermistor should be used.

Load Regulation And Efficiency Measurements

The first set of tests reveals the stability of the voltage rails and the PSU's efficiency. The applied load equals (approximately) 10 percent to 105 percent of the maximum load the supply can handle, in increments of 10 percentage points.

We conduct two additional tests. In the first metric, we stress the two minor rails (5V and 3.3V) with a high load while the load at +12V is only 0.10A. This test reveals whether the PSU is Haswell-ready or not. In the second test, we determine the maximum load the +12V rail can handle while the load on the minor rails was minimal.

Test12V (A/V)5V (A/V)3.3V (A/V)5VSB (A/V)PowerDC/AC (W)Efficiency (%)Fan Speed (RPM)Noise dB(A)In/Out (°C)PF/AC (V)

For an affordable PSU, load regulation is satisfactory. After all, the CS850M's main purpose is to offer decent performance at the lowest possible cost. On top of that, it manages to deliver full power for quite a while at high operating temperatures, proving that it can handle lots of heat in unfavorable environments. Still, we'd advise you to not operate the CS850M at high ambient temperatures for long if you want to keep it healthy.

As far as efficiency goes, the PSU easily clears the 80 PLUS Gold requirements at 20 and 50 percent of its maximum capacity, but it doesn't manage to sustain 87 percent under full load. Then again, we run our tests at high ambient temperatures, while the 80 PLUS organization uses an unrealistically-low 23 °C, resulting in lower energy losses and inflated efficiency readings.

At 40 percent load, the CS850M's noise remains under 40 dB(A), surpassing 45 dB(A) under 70 percent load. The fan is definitely audible under full load, though we had to push the power supply hard to make its cooler spin at full speed.

Aris Mpitziopoulos
Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.