Abstract: The present power supply has two step-up transformers with their respective primary and secondary windings series-connected. A half-wave rectifier tube and a filter are connected to the transformer secondary windings to rectify the current induced in them and to smooth out fluctuations in that current. One or more additional step-down transformers are provided, each having a primary winding that may be switched in series with the first-mentioned primary windings or disconnected from them and a secondary winding connected across a lamp. These additional transformers, when connected in the circuit, reduce the D.C. output voltage of the power supply and enable this output voltage to be selectively adjusted in steps. The lamps indicate visually which of these additional transformers are connected in the circuit.