In various aspects, ion sources, mass spectrometer systems, and a power supply circuit coupled to a feedback circuit are provided. A power supply is provided that includes at least the power supply circuit and is operable to transfer charge to a load. The feedback circuit is responsive to a DC component of an output voltage supplied by the power supply in a first feedback loop and an AC component of the output voltage in a second feedback loop to produce a feedback signal representative of at least one of: a value of the output voltage before a charge transfer from a capacitor of the power supply to a load; the value of the output voltage during the charge transfer from the capacitor of the power supply to the load; or the value of the output voltage after the charge transfer from the capacitor of the power supply to the load.