A switching power supply includes a source of DC voltage and a transformer having primary and secondary windings. A switching circuit is coupled between the DC voltage and the primary winding to provide alternating current to the primary winding. A rectifier circuit is coupled to the secondary winding to provide a DC output voltage. A controller circuit controls the switching circuit to modulate the alternating current provided to the primary winding. A circuit receives a first input signal having a magnitude which is determined by the DC output voltage and a second input signal having a magnitude which is determined by a selected position of a multiposition switch. An output of the circuit generates a feedback signal which is coupled to the controller circuit.