Articles: Cases/PSU

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UPS Compatibility

Working together with our SmartUPS SC 620, this PSU was stable at loads up to 374 watts when powered by the mains but couldn’t switch to the UPS’s batteries even at 280 watts.

Cross-Load Voltage Stability

The most important +12V voltage is very stable for a PSU that lacks dedicated voltage regulation. Each of our three reference PC configurations is in the 1% zone. In fact, the +12V voltage is never going to deflect by more than 2% from its required level in the typical load range.

The +5V voltage is the most stable at low loads. That's no problem since this voltage is no more than 2% off the required level at loads up to 50 watts on the +5 and +3.3V rails combined. Most computers don’t need more than that today.

The +3.3V rail is somewhat less stable, its voltage being the closest to the required level when there's high load on each power rail. The +3.3V voltage is 3% off at medium loads and 4% off when the computer is idle. Fortunately, this is the least used voltage in modern PCs.

Summing everything up, the HCG-620M delivers stable voltages, considering that it lacks dedicated voltage regulation.

Output Voltage Ripple

The high-frequency voltage ripple is low but there are occasional spikes on the +5V and +12V rails that shoot over the industry standard’s limits.

The same goes for the ripple at the double frequency of the mains, except that it’s now the +3.3V rather than the +5V rail that has occasional voltage spikes above the permissible limits.

In fact, this picture is similar to what we saw with the HCG-520 as well as with Seasonic’s original products.

Temperature and Noise

The HCG-620M is cooled by a 135mm 9-blade fan ADDA ADN512MB-A90. A large part of its impeller is covered with a piece of transparent plastic to optimize air flows.

The fan starts out at 900 RPM and retains this speed until a load of 300 watts. Then it accelerates quickly and linearly, reaching 1000 RPM at 350 watts and becoming rather noisy at loads above 400 watts. The maximum speed of the fan, somewhat higher than 2000 RPM, is achieved at 560 watts, and the fan keeps this speed until full load.

Thus, the HCG-620M is rather quiet at low and medium loads, but gets noisier than most competitors at high loads.

Efficiency and Power Factor

The HCG-620M is 86.4%, 87.7% and 84.3% efficient at the reference loads of 20%, 50% and 100%, respectively. It meets the requirements of the 80 PLUS Bronze certification whose badge it carries by a good margin.

The peak efficiency of 88.1% could be observed at a load of 256 watts.

The power factor remains as high as 99% through the larger part of the load range, which is an excellent result.

Standby Source

The standby source does its job without a problem.


The HCG-620M is a rather high-efficiency PSU with stable voltages and handy modular cables. The only downside in the electrical department is that it occasionally has high spikes of voltage. It is also noisy at high loads.

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