Abstract: This disclosure is concerned with adapting very high-voltage, low-current, high impedance power source circuits, such as CRT anode supplies and the like, to employ the efficiency over wide input voltage ranges and other advantages, including small size, of switching-mode operation through combining variable frequency (or period) output control circuitry with resonant high-voltage transformers, wherein the transformer resonant frequency is rendered comparable to the desired range of conversion frequencies; and in which resonant flyback circuit operation drives a voltage multiplier such as to accommodate the resonance caused by the stray capacitance shunting its storage inductance.