And that’s where I was really seriously disappointed. The PSU quickly passed the cross-load test at all allowable loads, but refused to sustain a load of 300W and higher for more than 3-4 minutes – the protection circuit would intervene. My attempts to squeeze this output power by varying the distribution of the loads on the different rails failed and… what’s this smell? My patience ran out sooner than the combustible materials in the PSU, so it was still alive when I shut it down – if you could call that “alive”. More exactly, I just didn’t turn it on again when it had automatically shut down at the fool load. The subsequent autopsy showed that a part of the plastic pipe that covered one of the output LC filter’s coils had burnt out.

By the way, I didn’t deflect the coil by 30 degrees from the normal to take a better snapshot – the coil was originally soldered awry!

Moreover, at a load of about 260-270W the power supply’s PFC coil emitted a low-frequency hum which was very irritating in combination with the buzz of the loose cover.

So I can only state that the maximum load power this power supply can be stable at is not higher than 250W, and it is absolutely impossible to make the HPU-3S350 stable at 300W.

The voltage ripple was as high as 46 millivolts on the +5V rail and 117 millivolts on the +12V rail and most of it is due to strong 100Hz pulsations (as shown in the second, 4msec/div oscillogram).

The efficiency of the PSU is not high, never reaching 80%, while the power factor is quite typical for a model with passive PFC.

The fan speed is linearly and quite effectively adjusted depending on the temperature of the PSU (I couldn’t measure the speed at the maximum output power due to the reasons explained above). Of course, the HPU-3S350 is not quiet. Its fan is easily audible at 200W load, but quiet operation cannot be demanded from a PSU of this category.

So, the Hiper HPU-3S350 is a very poor power supply with overtly overstated characteristics. There is no talk about 350 watts – the PSU can’t normally work under loads above 250W. Moreover, there’s a strong low-frequency voltage ripple and a poor cross-load characteristic; the thing is even assembled shoddily. You can get much better products for the price of a HPU-3S350 which is over $30.