a power supply and a method for providing in a convenient and inexpensive way an unlimited range of direct currents with superimposed alternating sinusoidal or non - sinusoidal currents to a single load or to a number of loads in parallel . a novel power supply derived from a conventional one by purposely unbalancing ac potentials of load terminals so that an additional ac voltage drop appears across the load . this unbalancing is accomplished through changing ac potentials of one or both lead terminals by connecting one of the terminals to different points along a special unbalancing transformer winding and / or by connecting capacitors between a load terminal and different points of this unbalancing winding .