The Fractal Design Ion+ 760P is a very quiet high-performance power supply of fine build quality. Its highly flexible cables, which lack in-line caps, make cable routing and management considerably easier. Costing about as much as PSUs with lower efficiency certifications, it also won't drain your wallet.
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