Abstract: A power supply system for supplying electrical power to at least one load includes a base plate, a support rail and a power supply module fastened to the base plate, at least one bus bar module, and a rail mounting device for mounting the bus bar module on the support rail. The rail mounting device includes conductor members for supplying power from the power supply module to bus bars contained within the bus bar modules, respectively. A first plug has contacts that engage contacts of each of the bus bars of the bus bar module via access slots contained in the cover member thereof, thereby to supply three-phase power to a load such, as a motor, via a heavy-duty power switch and a circuit breaker that are both mounted on the base plate, and associated second and third connecting plugs. Single-phase power is supplied to an auxiliary load, such as an electrical appliance, from two or more bus bars of the bus bar module via a fourth plug.