The utility model discloses a high stability tandem type switching power supply, including transformer W, rectifier bridge T, chip IC1 summation potential ware RP1, the both ends of 220V line voltage are connected respectively at transformer W's winding N1's both ends, and rectifier bridge T's port 1 and rectifier bridge T's port 3 are connected respectively to transformer W's winding N2's both ends, and electric capacity C4, resistance R1, diode D1's negative pole, triode V1's projecting pole and MOS pipe Q1's source electrode are connected to rectifier bridge T's port 2. The utility model discloses complicated chip structure has been abandoned to the high stability tandem type switching power supply circuit, only uses essential electronic component to constitute, has reduced the consumption and the cost of manufacture of circuit, increases electrical energy conversion efficiency to increase the undulant suppression component of commercial power in the circuit, can consequently have the advantage that low power dissipation, stable performance and cost of manufacture are low with the undulant spike voltage clamper that produces of commercial power to safe value.