Any source of electrical power in a form suitable for operating electronic circuits. Alternating-current power may be derived from the mains either directly or by means of a suitable transformer. Direct-current power may be supplied from batteries, suitable rectifier/filter circuits, or from a converter.

A bus is frequently employed to supply power to several circuits or to several different points in one circuit. Suitable values of voltage are derived from the common supply by coupling through dropping resistors or by capacitive coupling.