An exciter assembly for supplying a field current to the rotor windings of a superconducting synchronous machine includes a pulse transformer having a stationary primary winding and a secondary winding that is mounted to the rotor of the superconducting synchronous machine for rotation therewith. A switched mode power supply supplies a pulsed voltage to the primary winding of the pulse transformer. The pulsed voltage developed at the secondary winding of the pulse transformer is supplied to the rotor windings through a rectifier semiconductor device and a pair of transfer leads. The rotor windings and a flywheel semiconductor device are located inside a cryogenic chamber or cryostat. The flywheel semiconductor device is connected in parallel with the rotor windings and operates in unison with the rectifier semiconductor device in order to provide synchronous rectification of the switched mode power supply output. The switched mode power supply and both the primary and secondary windings of the pulse transformer are located outside the cryostat.