Abstract: The experimental studies of 400 kW PSM high voltage power supply are summarized in this paper. Firstly, the rapid protective method to shut down high voltage in 10 μs under over-current situation is described. The arc-deposited energy in the process of klystron breakdown is studied. The body-current waveforms of the klystron in different grounding modes are compared. The experimental results show that this type of all-solid state high voltage power supply has many advantages, such as the high anti-jamming capability, high efficiency and maintainability. It provides a highly beneficial path for high power vacuum microwave devices test.