A power supply system includes a transformer having a primary winding on its primary side for coupling to a power source and one or more secondary windings on its secondary side. A first control circuit is disposed on the primary side of the transformer for controlling a current flow in the primary winding. A second control circuit disposed on the secondary side of the transformer, and the second control circuit is configured to provide a regulated output voltage. In the power supply system, the first control circuit is configured to generate a control signal for controlling the current flow in the primary winding without using a feedback control signal from the secondary side of the transformer.