An electronic system and method include a controller to actively control power transfer from a primary winding of a switching power converter to an auxiliary-winding of an auxiliary power supply. The switching power converter is controlled and configured such that during transfer of power to the auxiliary-winding, the switching power converter does not transfer charge to one or more secondary-windings of the switching power converter. Thus, the switching power converter isolates one or more secondary transformer winding currents from an auxiliary-winding current. By isolating the charge delivered to the one or more secondary-windings from charge delivered to the auxiliary-winding, the controller can accurately determine an amount of charge delivered to the secondary-windings and, thus, to a load.