The present invention provides for a high voltage direct current power supply including a primary high voltage direct current supply offering a primary output; a floating secondary output floating with respect to the primary output and fed by the primary output: an output terminal at the floating secondary output for providing an output voltage; a controller operative to detect a change in the output voltage at the output terminal and to generate a control signal responsive to the change in output voltage; and a controllable current source, which can comprise a programmable current source, arranged to provide current at the floating secondary output responsive to the said control signal and whereby the said current is provided to reduce charging of a secondary output capacitance as the output voltage changes.