A power supply unit (PSU) is a component in a computer that provides power to the other components. It takes in AC power from a wall outlet and converts it to low-voltage DC power that is used by the components in a computer, such as the CPU, GPU, RAM, and storage devices. The PSU also regulates the voltage to ensure that each component receives the proper amount of power. The power capacity of a PSU is measured in watts, and the size of the PSU required for a particular system depends on the power requirements of the components in the system. A high-end system with multiple components will require a higher-wattage PSU compared to a basic system. A poor-quality or underpowered PSU can lead to stability and performance issues in a computer.