A power supply is a stand-alone device or assembly that supplies power to devices or assemblies that require voltages and currents other than those supplied by the electrical grid. Output voltage and maximum output current can be fixed or variable.

Power supplies are divided into switching power supplies and transformer power supplies, the latter still into regulated and unregulated. They are all available in different versions depending on the application. Usually they provide a DC voltage, but there are also AC voltages and rarely constant currents, also called constant current sources. They are needed, for example, for the operation of energy-saving lamps, semiconductor lasers or in chargers for charging accumulators. Universal laboratory power supplies can also be used in this operating mode.