Articles: Cases/PSU

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UPS Compatibility

Working together with my APC SmartUPS SC 620, this PSU was stable at loads up to 370 watts when powered by the mains but could only switch to the UPS’s batteries at 285 watts.

Cross-Load Stability

After the near-perfect performance of the Chieftec BPS in this test, the Cooler Master GX looks especially bad with its lack of dedicated voltage regulation.

The +12V voltage deviates very much at high loads on the +12V or the other rails. On the other hand, the deviation isn’t going to be higher than 3% with most real-life computer configurations.

The voltage on the +5V rail sags at high loads. As a result, the PSU cannot yield over 120 watts across the +3.3V and +5V rails combined without going beyond the permissible limits. In the typical load range this voltage is not going to deviate more than 2%, though.

The +3.3V voltage is good at low and medium loads, staying within 2% of the required level. It can go as far as 4% from that level at near-maximum loads, though.

So, the Cooler Master GX 750W is just satisfactory in terms of voltage stability, the only exception being the +5V rail. The PSU would lose the Power OK signal when there was a minimum load of 1 ampere on that rail, therefore we had to carry out our tests at a minimum load of 2 amperes. This must be a defect of the particular sample of the PSU, yet we have to report this disappointing fact.

Output Voltage Ripple

The high-frequency voltage ripple is not strong, yet there are occasional voltage spikes above the permissible limits on the +3.3V and +5V rails. We’ve seen the same behavior with many other PSUs based on Seasonic’s entry-level platforms (and this Cooler Master PSU isn’t the worst among them, we should note).

The same goes for the low-frequency ripple except that the voltage spikes are not so high.

Temperature and Noise

This PSU is cooled by a 7-blade Young Lin Tech fan (DFS122512H, 3000 RPM, 120 mm).

The fan starts out at a speed of 1000 RPM and maintains it until a load of 400 watts. Then it accelerates in a linear manner. The top speed is as high as 1500 RPM at full load. Having a smaller fan working at a lower speed, the Cooler Master turns out to be somewhat quieter than the above-discussed Chieftec but the fan’s behavior is overall the same.

Efficiency and Power Factor

The power factor is somewhat lower than what you can expect from a PSU with active power factor correction, but that’s not important for home users.

The efficiency is okay, too. The PSU meets the 80+Bronze requirements. Its efficiency was 86.7%, 87.6%, 82.2% at loads of 20%, 50% and 100%, respectively. Its peak efficiency was 88.6% at a load of 265 watts.

So, the Cooler Master GX 750W is highly efficient at low and medium loads but loses in efficiency at full load more than the above-discussed Chieftec does. The latter PSU was more consistent in this test.

Standby Source

The standby voltage is somewhat higher than necessary at any load, but meets the requirements of the industry standard.


The Cooler Master GX 750W is a rather quiet PSU with acceptable electrical parameters and a rich selection of peripheral power connectors. However, it offers only two graphics card connectors, which doesn’t seem enough for its wattage, and its CPU power cable is too short.

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