Many tube power supplies in use in high-energy physics accelerator systems are based upon 50/60Hz, line frequency technology which demands large transformers, capacitors and filters in order to satisfy the stringent specifications. These systems have huge amounts of stored energy and require crowbars for tube protection. Generally, high power supplies for RF modulators have not fully exploited and kept pace with the latest developments in power electronic technology. The PEMC Group at Nottingham has been applying expertise gained from many other application areas to research, develop and experimentally validate leading-edge power electronics technology for high power RF modulator power supplies. These developments are based on resonant converter technology, allowing high frequency switching at high power, with a consequent reduction in size and stored energy. This seminar will review the research to date and will discuss results obtained from practical prototypes. Applications for the technology outside the accelerator field will also be briefly discussed.