A high voltage DC power supply for an electrical field treater which includes a hermetically sealed metal enclosure filled with transformer oil immersing a removable rack. The rack has a high voltage transformer mounted upon a base and a vertical guideway receiving one or more voltage multiplier modules which can be inserted therein in only one orientation. Terminal connectors are provided upon an insulated base mounted on the rack and each voltage dc power supply multiplier unit carries superimposed and subtended complementary terminal connectors. Voltage multiplier units can be readily mounted within the rack for increasing proportionately the DC voltage output of the power supply. The uppermost voltage multiplier module carries a superimposed connector which permits receipt of a mating connector at the end of a flexible lead for conducting high potential current to a high voltage bushing mounted in the wall of the metal enclosure. This arrangement permits the ready installation of the power supply on an electrical field treater, facilitates repairs and simplifies changing the output DC voltage as desired.