A power supply is a device that supplies power to another device, at a specific voltage level, voltage type and current level. For example, when we talk about a 9VDC @ 500mA power supply can provide as much as 500mA of current and the voltage will be at least 9V DC up to that maximum current level. While it sounds simple, power supplies have a lot of little hang-ups that can be very tricky for the uninitiated. For example, unregulated supplies say they can provide 9V but really may be outputting 15V! The very common 7805 regulator datasheet claims it can regulate up to 1000 mA of current, but when you put a 15V supply on one side, it overheats and shuts down! This tutorial will try to help explain all about power supplies.