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 internal components, such as the motherboard and hard drives, require to function properly. PSUs come in various wattages to accommodate different power needs, and they often include features like over-voltage protection and cooling fans to ensure safe operation. A reliable PSU is essential for maintaining the performance and longevity of a computer or any electronic system.