Abstract: An RCC-type switching power supply has a main switch means 9 which is repeatedly rendered conductive and cut off to cause a switching current to flow through a primary winding 31 for transferring energy from a primary side to a secondary side due to flyback operation. A snubber circuit 5a.about.5c has a snubber capacitor 7 and an auxiliary switch means 3 which are connected in series with each other and parallel to the primary winding 31. When the auxiliary switch means 3 is rendered conductive by an auxiliary winding 4 when the main switch means 9 is cut off, the auxiliary switch means 3 first effects third-quadrant operation to charge the snubber capacitor 7 with energy stored in a leakage inductance of the primary winding 31, and then effects first-quadrant operation to discharge the snubber capacitor 7 to cause a current to flow through the primary winding 31.