But the 550W Kingwin won't spin below 400W at all. The fan is just a fail safe device.
1. I was responding to your post about fan spinning at low loads. I correctly pointed out that the Seasonic does not spin at low loads either.
2. The Seasonic does spin in "silent mode" at about 16 db (according to Seasonic) between 20-50% load. Obviously, 16 db is not completely silent, but unless once is operating a recording studio, I don't think one would hear it at normal distances. Above 50% load, it starts to ramp up (in what you might call fall-safe mode). These numbers will be adjusted automatically by the PSU if ambient temperature exceed 25C.
3. Seasonic does make two very simular X-Series PSU's with no fan at all
(X-400/460) if that is what is needed, but very few people would hear the X-560/660/760 fan over the noise of GPU fan, music, or whatever, if their PSU was running above 50% load.