500 Watts power supply for 10 dollars?

There are power supplies that can be gotten that cheap, but they're usually low quality and lacking safety features, likely even fire hazards. Watch BadActor's YouTube video, if drapes had been right behind some of those he could have had a fire.

I recommend the Cooler Master V series, Corsair RM/RMx/RMi AX/AXi series, and the EVGA Supernova G2/P2/T2 series of power supplies.