High voltage direct current power supplies having both of the following characteristics: a. Capable of continuously producing, over a time period of eight hours, 10 kV or more, with output power of 5 kW or more with or without sweeping; and b. Current or voltage stability better than 0,1 % over a time period of four hours. Note: This item does not cover power supplies defined in items 0B001.j.5 and 3A227.