The PSUs comply with the EPS12V and ATX12V 2.2 standards. The load capacity of the +5V and +3.3V rails isn’t high for their wattage, but the modern standards do not demand that. Instead, the PSU can yield almost of all its output power on the +12V rail alone. Well, there’s only a 50W increase of the allowable load power on the +12V rail with the senior model whereas its overall wattage is higher by 100W.

The ST75ZF worked normally with an APC SmartUPS SC 620 at loads below 360W from the mains and at loads below 320W from the batteries. The numbers are both 5W lower with the ST85ZF.

The PSUs come with the following cables and connectors:

• Mainboard cable with a 24-pin connector (55cm long)
• CPU cable with an 8-pin connector (55cm long)
• Additional mainboard cable (AUX) with a 6-pin connector (55cm)
• Two (for with the ST85ZF) graphics card cables with 6-pin connectors (55cm each)
• Two cables with two Molex connectors and one floppy mini-plug on each (52cm from the PSU case to the first plug, 25cm more to the second Molex and 15cm more again to the floppy plug)
• Cable with two Molex connectors (52cm+25cm)
• Two cables with two (three with the ST85ZF) SATA power connectors on each (52cm+26cm)

The cables are all sleeved, except for the cables you connect to your optical and hard drives.

At a load of 840W the voltage ripple was 25 millivolts on the +5V rail, 39 millivolts on the +12V rail, and 28 millivolts on the +3.3V rail. I drew two markers in the oscillogram, at the maximums of pulsations on the +5V and +12V rails. It’s clear that the pulsations are not synchronized. This is a consequence of the use of fully independent PWM regulators on the different power rails of the PSU.

Both PSU models have excellent cross-load characteristics – the diagrams are almost all green. The certain spottiness is due to the influence of the high-frequency (400 kHz – we’ve never tested PSUs with a frequency of over 130 kHz) pulsation of the PSUs’ output voltage. We’ll add additional filters to our testbed for future tests.

Identical San Cooler 80 fans, the 9A0812S413 model, are installed in both PSUs, but in the junior model the fan would emit an irritating hiss at a speed of over 2400rpm while the senior model was surprisingly quiet, for its class. Perhaps there is just a defective sample of the fan in our ST75ZF.

The fan speed grows steadily up within a load range of 200 to 600W and then becomes constant at 3350rpm. Of course, there’s no talking about silence here. The whisper of the air passing through the PSU is perfectly audible, yet I had feared an even worse result. The ST85ZF is quite acceptable with its noise characteristics. The ST75ZF may be improved by replacing its native fan with another sample.

The efficiency of the PSUs got over 87% at a load of 200W and reached a record-breaking 80% in the end (the difference between the two models is less than 1%). At low loads, however, the efficiency degenerates catastrophically, to 50% and 51% at a load of 50W. Well, you will hardly buy an 850W power supply costing a few hundred US dollars to install it into a low-end computer while a serious gaming station with top-end graphics cards consuming 30-40W each even in idle mode can hardly have a power draw of less than 100W. At loads of about 150W, the Seasonic PSUs are a mere 5% behind the FSP models.

So, the two new power supplies from the Zeus series leave a nice impression on me, even though I can hardly imagine a computer that would require as much juice. If your computer doesn’t need that much, you may want to buy a simpler and quieter PSU and save some money at that. But in their class both the Zeus models are very good, with superb voltage stability, high efficiency, rather quiet operation, high quality of manufacture and the availability of all the connectors you may need.