Power supplies are devices that produce AC or DC power.  This grouping includes current sources, DC power supplies, AC-DC adapters, DC-DC converters, AC power sources, and DC-AC inverters. Current sources provide reliable current for electrical component testing and for powering specialized components.  DC power supplies accept AC input and provide one or more DC outputs for a wide variety of computer and industrial applications.  AC / DC adapters accept AC input voltage directly from a wall outlet, and output DC voltage. DC-DC converters accept DC input and provide regulated DC outputs for computers, telecommunications, and process control applications. AC power sources provide alternating power and will typically have adjustable output values for the testing of component response at various voltage, current and frequency levels. DC to AC power inverters are used for converting direct current (DC) into alternating current (AC). They are also known as DC to AC converters.  Rectifiers accept AC input and provide one or more DC outputs for a wide variety of computer and industrial applications.  Style, output, display, application, and features are all important to consider when specifying power supplies.

Choices for power supply style include ATX, board, cabinet, desktop, DIN rail, module, open frame, enclosed, PCB mount, rack mount and wall mount.  Important output specifications to consider include number of outputs, DC output voltage, DC output power, AC output voltage, AC output frequency and apparent power.  Common choices for DC output voltage include 3.3 V, 5 V, 12 V, 15 V, 24 V, and 48 V.  The DC output power is the output power of the device.  Power supplies can also have an AC output voltage as well as AC output frequency.  Apparent power is the product of the RMS current and the RMS voltage of the AC output, it is identical to the VA rating.

Display choices include analog visual indicators, digital numerical displays, and graphic or video displays.  Common applications for power supplies include computer, high current, high frequency, high voltage, instrumentation, laser, magnetic, medical, military, plasma, telecommunications, and testing equipment.  Common features for power supplies include adjustable voltage, adjustable frequency, computer interface, fan cooled, integral heatsink, overcurrent protection, overvoltage protection, power factor correction, pure sine output, remote on or off switch, short circuit protection, and water cooled.  An important environmental parameter to consider when specifying power supplies is the operating temperature.