Shielded electrical transformers and power converters using those transformers are disclosed. In some implementations, a shielded electrical transformer includes a magnetic core, a primary winding, a first secondary winding, and a second secondary winding. The transformer includes a first shielding winding that has a same voltage potential direction as the primary winding and is connected in series with the primary winding to carry current that passes through the primary winding. The transformer also includes a second shielding winding that has a voltage potential direction opposite the primary winding and is connected from primary ground to a floating terminal. The first secondary winding, the second secondary winding, the first shielding winding, and the second shielding winding can each have an approximately equal number of turns.