The textbook sets out the theoretical foundations of power supplies for technological machines and equipment. The processes occurring in the welding arc, static and dynamic current-voltage characteristics of the welding arc are given. Welding properties of sources and methods of their assessment are considered. The device of welding transformers for general industrial purposes is described. The device and descriptions of promising sources of the welding arc are presented. This textbook is intended for students of 60720700-Technological machines and equipment (mechanical engineering, metalworking) and bachelors of mechanical engineering of other universities, including masters, college students, can also be used by technologists and designers of manufacturing enterprises.