Abstract: A multiple output switching power supply wherein the voltage at a main output which couples to a main secondary winding of a transformer is regulated by pulse width modulation of the current flowing in the primary winding of the transformer and wherein the voltage at an auxiliary output which couples to an auxiliary secondary winding of the transformer is regulated by pulse width modulation of the current flowing in the auxiliary winding. The pulse width modulation is performed in synchronism with a preestablished turn-on delay of the control switches which control current pulses in the primary winding as to the turn-on of the switches which control current pulses in the auxiliary winding. Besides avoiding the need for a filter between the auxiliary winding and the related control switch, this form of synchronization reduces switching power losses, current spikes and induced radio frequency emission.