A power supply assembly which can drive a number of different devices at different voltages. A rack holds a number of breaker modules, and each breaker module can connect to one or many breakout boxes. The breakout boxes are keyed to the breaker modules, so that the breaker boxes will not be energized with power unless they are the proper voltage and/or configuration to receive that power. The coil of a contactor in the breaker module is powered by a key wire that is connected through specified pins in the breakout box. Therefore, no power is ever provided to the breakout box unless it is of the proper voltage configuration. In addition, feeder power to the power supply assembly is provided over bolted connections, without any wire connections between the power feed and the circuit breaker.