Working with our APC SmartUPS SC 620, this PSU was stable at loads up to 380 watts when powered by the mains and could switch to the UPS’s batteries at a load of 290 watts.
Cross-Load Voltage Stability
The manufacturer claims that the Nightjar series PSUs keep their voltages within 3% of the required levels and our measurements almost agree with that claim.
Like with the previous PSUs, we can see no problems about the +12V and +5V voltages. They are always within 2% of the required levels.
And like with the previous products, the +3.3V rail is the least stable of all. This voltage can be up to 5% off the necessary level. On the other hand, it is indeed within 3% in the typical load range. In fact, the Nightjar SST-ST50NF is the best of the four PSUs in terms of the +3V voltage at typical loads.
Output Voltage Ripple
The output voltage ripple isn’t strong but there are occasional spikes above the permissible limits on the +5V and +12V rails.
The same goes for the low-frequency voltage ripple, but the occasional spikes aren’t that high here.
Efficiency and Power Factor
The Nightjar SST-ST50NF was 84.9%, 88.9% and 88.7% efficient at the reference loads of 20%, 50% and 100%. This confirms its 80 PLUS Bronze certification. The PSU just lacks a little at 20% load to meet the Silver requirements.
The peak efficiency of 89.9% was achieved at a load of 286 watts. The Nightjar SST-ST50NF couldn’t hit 90% at any point of the graph.
The power factor is about 99%, which is an excellent result.
As expected, the standby source is okay, although its voltage is almost 3% higher than necessary at the minimum load. That’s more than with the other PSUs, but within the requirements of the industry standard.
Based on the oldest platform among the four tested PSUs, the Nightjar SST-ST50NF is still quite a competitive product. It delivers stable voltages and features an overheat indicator. However, it is inferior to its younger opponents in terms of efficiency and output voltage ripple.