A power supply is a switch with on and off supply designed to convert 110-240 V AC power from the mains supply, to several output both positive (and historically negative) DC voltages in the range + 12V,-12V,+5V,+5VBs and +3.3V. The first generation of computers power supplies were linear devices, but as cost became a driving factor, and weight became important, switched mode supplies are almost universal. Some of the most common issue are that the system will not charge anymore, it must always be plugged in, does not fully charge, or have to wiggle the power cord so it can charge again. Which ever the case may be we can diagnose and repair the problem.