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.
A power feed for a submarine communications system includes a plurality of power converters each of which has at least 2 step-up transformer stages in which at least one of the windings of at least one of the transformer stages of at least one of the plurality of power converters is wound using a high voltage insulating wire to insulate against a high DC voltage appearing at an output of an adjacent power converter. The use of high voltage insulating wire removes the need for expensive custom built DC blocking capacitors.
