A welding power supply is a device that provides or modulates an electric current to perform arc welding. There are multiple arc welding processes ranging from Shielded Metal Arc Welding (SMAW) to inert shielding gas like Gas metal arc welding (GMAW) or Gas tungsten arc welding (GTAW). Welding power supplies primarily serve as devices that allow a welder to exercise control over whether current is alternating current (AC) or direct current (DC), as well as the amount of current and voltage.
Power supplies for welding processes that use shielding gas also offer connections for gas and methods to control gas flow. The operator can set these factors to within the parameters as needed by the metal type, thickness, and technique to be used. The majority of welding power supplies do not generate power, instead functioning as controllable transformers that allow the operator to adjust electrical properties as needed. However, in some welding applications, notably SMAW, used in areas isolated from power grids, welding power supplies are used that combine the functions of electrical generation and current modulation into a single mobile unit mounted on a vehicle or towed trailer.