power supply

A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (e.g., mechanical, chemical, solar) to electrical energy. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source.
Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from:

• Electrical energy transmission systems. Common examples of this include power supplies that convert AC line voltage to DC voltage.
• Energy storage devices such as batteries and fuel cells.
• Electromechanical systems such as generators and alternators.
• Solar power.

A power supply may be implemented as a discrete, stand-alone device or as an integral device that is hardwired to its load. In the latter case, for example, low voltage DC power supplies are commonly integrated with their loads in devices such as computers and household electronics.
Constraints that commonly affect power supplies include:

• The amount of voltage and current they can supply.
• How long they can supply energy without needing some kind of refueling or recharging (applies to power supplies that employ portable energy sources).
• How stable their output voltage or current is under varying load conditions.
• Whether they provide continuous or pulsed energy.