Kingwin Stryker Fanless 500 W
 

The Kingwin Stryker 500 W is an amazing little PSU. It is one of the few models that offers 80PLUS Platinum efficiency, which means well over 90%, even at low load. In addition to that the power supply is completely fanless, emitting no noise at all - great for a quiet office PC or media PC system.

http://www.techpowerup.com/reviews/Kingwin/STR-500/