A high voltage power supply having energy storage, charging and switching elements and using an interruptible switch as the switching element for efficient, compact and safe operation. In a specific embodiment, the interruptible switch is implemented with at least one cold cathode grid-controlled, crossed field plasma switch and associated control circuit. The charging element is a Marx bank which can be capacitive or inductive. A single control circuit may be used in a master-slave configuration for the capacitive and inductive Marx bank implementations. A pulse forming network can be used in connection with a cold cathode grid-controlled, crossed field plasma switch to provide a regulator for the power supply. In the inductive embodiment, the field plasma switch may include plural switching elements in a single envelope, each switching element including a cathode, a control grid and an anode, the cathode of at least one switching element being the anode of the next switching element and so on. A current amplifier and voltage regulator is implemented with a cold cathode grid-controlled, crossed field plasma switch having a cathode, an anode and a control grid therebetween.