A power supply unit is a stand-alone device or assembly for supplying power to devices or assemblies that require different voltages and currents than are provided by mains supply. The output voltage and maximum output current can be fixed or variable.
Power supply units are divided into switching power supplies and transformer power supplies, the latter is further divided into regulated and unregulated. They are all available in different versions depending on the intended use. Mostly they provide a DC voltage, but there are also those for AC voltage and, rarely, those for constant current, also called constant current source. They are needed, for example, to operate energy-saving lamps, semiconductor lasers or used in chargers to charge accumulators. Furthermore, universal laboratory power supplies can be used in this operating mode.
