Abstract: A switching power supply in which the maximum power output is limited during various line voltages within a predetermined range on a cycle by cycle basis. The power supply comprises a transformer in which an alternating current voltage is applied across the primary winding thereof. Switching means are connected in series with the primary winding. The repetitive conduction and non-conduction of the switching means controls the flow of current in the secondary winding circuit of the transformer for producing a direct current output voltage in the secondary winding circuit. Output voltage is produced in the secondary winding circuit during the interval the switching means is not conducting. For limiting the maximum power output in the secondary winding circuit during various line voltages, a control circuit controls the maximum conduction time of the switching means in response to the rectified voltage appearing across the primary winding of the transformer.