Abstract: A constant-voltage transformer for stabilized power supply includes a primary coil and a secondary coil connected across a tuning capacitor. A magnetically continuous magnetic core links both the primary coil and the secondary coil, and a magnetically discontinuous magnetic core links the secondary coil but not the primary coil. Another discontinuous magnetic core may link the primary coil but not the secondary coil, and a compensating coil may be linked by this core only. Preferred designs have an abrupt cut-off at a load current only a little greater than design value, so that a dangerously high current can never be drawn, even into a total short circuit.