A Power Supply Unit (PSU) is a crucial component in computers and electronic devices that converts electrical power from an outlet into usable power for the device. It takes the high voltage alternating current (AC) from the wall and transforms it into low voltage direct current (DC) that the computer's components, like the motherboard and graphics card, require to function properly. PSUs come in various wattages to accommodate different power needs, ensuring that all components receive adequate energy. They also include safety features to protect against power surges and overheating, which can damage sensitive parts. Proper selection of a PSU is essential for system stability and performance.