Power supply unit

A power supply unit (PSU) is an electronic module that converts (ranging from 100 or 240  at 50 to 60 Hz)   into a smoothed direct current at the various different voltages required by the computer motherboard, internal storage devices (such as hard disk, SSD, CD, DVD, or floppy disk drives), and external peripheral connections such as USB.

Description
A power supply unit needs a high enough power output rating to supply all the devices connected to it and should output as little as possible, both on the output wires and as. A larger computer may have a completely self-enclosed PSU, while a smaller model or laptop may use an external power adapter, sometimes referred to as a "power brick". Very small mobile devices may use chargers with compact power supplies built into the wall plug, sometimes referred to as "wall warts".

History
Rod Holt designed Apple Computer's first internally-developed power supply unit for the Apple II, which was released in 1977 without a fan at the insistence of Apple co-founder Steve Jobs.