the power supply unit in a computer converts the power from the wall outlet to the type of power needed by the computy. it sends power through cables to the mortherboard other components.if you decide to computer case and take a look , make sure to unplug the computer first. before touching the inside of the computer , you should touch grounded metal object-or a metal part of the computer casing - to discharge any static buildup. static electricity can be transmitted through the computer circuits and ruin them.