If you want a computer to truly be silent, you need to use passive cooling components. Whereas passive cooling components are more frequently available in the graphics card and CPU sector, they are something of a niche market when it comes to power supplies. This is not really a surprise though, given that purely passive units are considerably more expensive than those with fans, and they generally provide relatively poorer performance as well.
Our test compares the Zen 400 from Fortron (FSP) with a power output of 400 watts, and the Nightjar 450 from Silverstone which provides a maximum of 450 watts. Both models can be purchased for less than $200.
In order to ensure proper comparison of the units—and in anticipation of future testing with other units having different power output levels—we tested the efficiency at 100%, 50% and 20% load. In the future, we will also be testing the efficiency at an output of 250 watts, as well as an extremely low output of just 35 watts. The latter is of particular importance for low power systems, to ensure that users are able to find the right kind of power supply for these as well.