Abstract: A power supply for a gamma radiation detector, or other detector device electrically detecting the aperiodic occurrence of a phenomenon, comprises a free-running oscillator periodically outputting, at a low repetition rate, pulses having short widths and long intervals between them; a capacitor chargeable to the detector operating voltage for operating the electrical detector device; a charging circuit coupling the oscillator to the capacitor for charging same by the pulses periodically outputted by the oscillator, the capacitor being partially discharged by the detector device upon a detection of the phenomenon; and an oscillator control effective, upon a detection of the phenomenon by the detector device, to trigger the oscillator to immediately output a pulse for recharging the capacitor.