An improved regenerative control type power supply device having a higher efficiency is disclosed. The power supply device has: a first switching elements which is connected in series with the primary winding of a transformer (this series circuit is connected to the terminals of a DC power source); a second switching element; a capacitor which is connected in series with the second switching means (this series circuit is connected to the primary winding); a rectifying and smoothing circuit for rectifying and smoothing a flyback voltage which generates in the secondary winding and for outputting a resulting DC voltage; and a drive circuit for driving alternately the first and second switching means with predetermined ON-OFF periods.
