The present invention is associated with a power adapter capable of simultaneously providing a low-level DC voltage and a high-level DC voltage. The power adapter includes a transformer having a primary winding for storing energy when a main switch coupled therewith is turned on and transferring the stored energy to the secondary side of the transformer when the main switch is turned off. The transformer includes a first secondary winding and a second secondary winding connected in series with each other. A first rectifier/filter circuit is connected across the first secondary winding for generating a low-level DC voltage by rectifying and filtering the energy received by the first secondary winding, and a second rectifier/filter circuit is connected across the first secondary winding and the second secondary winding for generating a high-level DC voltage by rectifying and filtering the energy received by the first secondary winding and the second secondary winding.