When the PSU was working with an APC SmartUPS SC 620, a load of 360W and 345W for the mains and batteries, respectively, was the highest allowable for the PSU. The switching to the batteries was performed without problems.

At loads higher than 300W a choke would begin to buzz quietly in the PSU. I had to put my ear next to the PSU case to hear it, though.

Apart from the short-term spikes at the moments of switching the transistors, which are going to be effectively filtered out by the mainboard, the voltage ripple at a load of 470W was 30 millivolts on the +5V rail, 50 millivolts on the +12V rail and 23 millivolts on the +3.3V rail. The PWM controller works at a frequency of about 130kHz.

The cross-load diagram of this power supply looks perfect. It’s all green except for the +3.3V voltage going into yellow a little. All the voltages are going to be rock-solid under the conditions of a real computer system.

The PSU makes use of an Adda AD1212MB-A71GL fan whose speed is kept at about 750rpm until a load of 250W. Then the speed begins to grow, reaching a mere 1150rpm at 470W. That’s a recording-breaking result, by the way. The fan speed is going to be somewhat higher in a hot system case, yet it anyway won’t be as high as in the PSUs described earlier in this review. The S-12 is one of the quietest power supplies ever tested in our labs!

The SS-500HT also boasts a very high efficiency: 86% at high load and a little lower at low loads. It is going to be about 83% under real-life conditions. The S-12 doesn’t comply with the 80 Plus program because its efficiency is lower than 80% at a 150W load. Well, Seasonic has a special version of this PSU that is declared to meet that requirement. Perhaps its efficiency graph would look better.

So, the S-12 has gone through our test program with ease. It offers all the connectors you may need, its output voltages are rock solid, its fan is very quiet, and its efficiency is always higher than 80%. The only thing I may want to improve in this PSU is to lower its voltage ripple, especially the short spikes at the moment of switching the inverter’s transistors, but this is hardly a serious defect. This won’t affect the stability of the system in any way.