Power supplies form an integral part of the electro-mechanical world. From a broad perspective, their primary function is to provide electric energy to all types of electronic circuits (e.g. small electronic devices, large machinery) in both the commercial and industrial worlds. From a narrower perspective, their primary function is to power electrical circuits by converting or adapting one form of electrical power into another.

Grasping the parallel understandings of the term power supply is key in order to clarify the confusing terminology which often surrounds this subject. According to the broad definition, virtually every electronic device carries a component that can be identified as a “power supply” (e.g. flashlights containing batteries). It is important to note, however, that the term power supply strongly carries the connotation of converting pre-existing electric power into a more suitable form for a specific application. Oftentimes components identified as “power supplies” are physically integrated into the device or circuit the power (although independent units definitely exist).

One of the most common examples of a power supply is the adaption of electrical circuits to power computers. Ironically, this application can be a source of further terminological confusion. A power supply unit (PSU) converts alternating current to direct current (discussed below) for a computer while a power brick refers to a specific type of standalone converter for laptops. Both of these terms, however, are sometimes applied to the more general idea of a power supply. Similarly, the term power adapter technically refers to a component that converts a power supply by physically enabling a device to fit into a terminal with an otherwise incompatible shape. However, the label is sometimes indiscriminately applied to power supplies in a more general sense.