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.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips