Conclusion: best choice 500/550 watts
For each part of the test we mentioned various models that stood out in a positive or negative way. When we filter out all power supplies with clear downsides, we are left with 19 out of 43 PSUs that are potentially worth buying. The question then remains, which one is the very best choice out of those 19?
In the segment below 600 watts, the Seasonic X-560 is clearly the best power supply: semi-passive (which means inaudible), very efficient (88.8 percent on average), low ripple (43.6 mVtt at 500W), stable voltages (min. 11.93V at 500W), modular and sufficiently long cables. There is really nothing to complain about. With a price of £109 it's not cheap, but that's to be expected with such quality.
Out of the more affordable models, our preference goes to the Nexus NX-5000 R3 530W and XFX Pro 550W Core. The Nexus is somewhat more quiet (max 32.1 dB), more efficient (86.2 percent) and has longer cables. The XFX is a little cheaper, and has a lower ripple. The Cooler Master Silent Pro M2 520W costs £77 which is a good price for this interesting modular alternative.
Seasonic X-Series 560W
Nexus NX-5000 R3 530W
XFX Pro 550W Core Edition
Cooler Master Silent Pro M2 520W