An active element that provides a specific voltage or current that is completely independent of other circuit elements.
Basic circuits textbook
A piece of test equipment used to supply DC voltage and current to electronic circuits under test.
Grob’s Basic Electronics, 11th Edition by Mitchel E. Schultz
A circuit that converts ac line voltage to DC voltage and supplies constant power to operate a circuit or system
Electronic Devices : Conventional Current Version, 9th Edition by Thomas L. Floyd