PURPOSE: To lighten the burden of a capacitor by a method wherein two sets of windings of transformers for two sets of DC/DC converters connected in parallel are connected so that the primary sides are connected in parallel to open and close in opposite phase while the secondary sides of the same are connected in series to equalize the burdens of the transformers.

CONSTITUTION: Two sets of DC/DC converters are constituted of switching transistor units 13, 14, power converting units 15, 16 and rectifying and smoothing units 17, 18. Transformers T1, T2, T3, T4, constituting the power converting units 15, 16, are provided with the same structure and the primary coil is equipped with two windings (n1) but the secondary coil is equipped with two windings (n2) while the windings (n1) are connected in parallel and the windings (n2) are connected in series. The windings (n1) of the transformers T1-T4 are controlled by a controller, not shown in a diagram, and are put ON/OFF in phases by the switching transistors 13, 14. The positive poles and the negative poles of the rectifying and smoothing units 17, 18 are connected in parallel while a current is supplied to a load 20 through a smoothing capacitor 19. According to this method, the burdens of the transformers T1-T4 are equalized and the burdens of the smoothing capacitors 12, 19 are lightened.