A pulse width modulated soft-switching power converter has a transformer with a primary winding and a secondary winding, a secondary circuit coupled to the secondary winding, and a pair of main switches and a pair of auxiliary switches coupled to the primary winding. The main switches and auxiliary switches intermittently conduct an input voltage source to the primary winding of the transformer to operate the soft-switching power converter in four operation stages in each switching cycle. The main switches conduct the input voltage source to the transformer in a first operation stage. In a second operation stage, the conduction is cut off. The transformer operates as an inductor with the auxiliary switches switched on under zero-voltage or zero-current switching mode in a third operation stage. In the fourth operation stage, auxiliary switches are switched off to achieve zero-voltage transition.