AC: alternating electric current (current that reverses direction)

AC power supply: a PSU that generates an AC output voltage (also called power inverter).

Convection-cooled power supply: a PSU that is cooled from the natural motion of an air over the surfaces of its components.

DC power supply: a PSU that produces DC output voltage, i.e. a voltage of a fixed polarity and specific value (which can be variable though).

External power supply: a PSU that is located outside of an equipment and can sometimes power more than one electronic device

Generators: devices that convert energy from mechanical form to electrical form.

Isolating power supply: a PSU that provides isolation between input and output.
See also: Isolation.

Isolation: absence of DC current pass between two circuits. In a PSU isolation is provided by transformers. Commercially available AC-DC PSU are normally isolating. Low input voltage DC-DC PSU, such as car phone chargers, are often non-isolating. Note that isolation does not necessarily mean a complete absence of current path- some low-level AC currents can still flow from input to output through physical and/or stray capacitances.

Linear power supply: a PSU that regulates an output parameter (usually output voltage) by varying voltage drop across an electronic component placed in series with the load. This component dissipates unused power and it may be a transistor or a resistor. The regulation is accomplished by changing the effective resistance of the series pass element or by forcing extra current through this element.

Off-line power supply: a PSU that processes electric power from AC line without using line frequency transformer. Such supply can still be isolating if it uses high-frequency transformer in one of its power conversion stages. A typical off-line SMPS rectifies input AC line voltage, produces high-frequency pulses by using semiconductor power switches, changes the voltage level by using inductors and/or transformers, then rectifies it again and filters for DC output. An example of isolating off-line PSU is a switching power supply of a computer.

PARD: Periodic and Random Deviation from the power supply's output DC voltage. Includes ripple and aperiodic noise. PARD is usually expressed in mV peak-to-peak or rms, at a specified bandwidth, typically 20 MHz.

Power supply: a device that transfers electric energy from one form to another using electronic circuits. It is also called Power Supply Unit (PSU). A common application of power supplies is to convert mains AC power into low-level DC voltages required for electronic equipment. Unlike generators, it does not need any moving parts.

PSU: see Power supply.

Regulated power supply: a PSU that maintains a given output parameter (usually voltage) to within specified limits under varying operating conditions, such as input line, output load, and ambient temperature.

SMPS: see Switching power supply

Switching power supply (switch mode, or SMPS): a PSU that incorporates power transistors that are continuously switching on and off with high frequency in order to provide the transfer of electric energy. An output parameter (usually output voltage) is controlled by varying duty cycle, frequency or a phase shift of these transitions. SMPS frequency can vary typically from 50 kHz to several MHz.

Uninterruptible power supply (UPS): a PSU that continues to supply electricity to the load for limited periods of time during a loss of utility's power or when the line voltage varies outside normal limits. UPS is normally implemented with a backup battery, charger and a DC-AC inverter.

Universal input power supply: a PSU that can operate at AC line voltages found anywhere in the world (typically from 90 to 264 VAC).

Voltage converter: technically it can be the same as a power supply, except the term "converter" is often used for a single-stage switching regulator. A typical off-line SMPS may consist of several cascaded voltage converters. The term converter also often implies that it is a sub-assembly of PSU, which may need additional components (such as EMI filters, protective devices, housing, etc.).