A power supplying device includes: an output transformer including first and second output coils for generating first intermediate voltages from an input voltage; a voltage adjusting transformer including primary and secondary coils; a first rectifying-and-filtering circuit connected to the first output coil for generating a first output voltage from the first intermediate voltage obtained from the first output coil; the primary coil being connected in parallel to the first output coil, the secondary coil being connected in series to the second output coil and being coupled to the primary coil for generating a second intermediate voltage from the first intermediate voltage obtained from the first output coil; and a second rectifying-and-filtering circuit connected to the secondary coil for generating a second output voltage from a combined voltage combining the second intermediate voltage obtained from the secondary coil with the first intermediate voltage obtained from the second output coil.