A coaxial capacitor array can include a plurality of capacitors arranged in at least one concentric ring around a longitudinal axis, an inner conductive element positioned at a center of the at least one concentric ring and electrically connected to first terminals of the plurality of capacitors, and an outer conductive element positioned around an outer periphery of the at least one concentric ring and electrically connected to second terminals of the plurality of capacitors. The concentric arrangement can produce opposing currents in the inner and outer conductive elements that generate magnetic fields that substantially cancel, resulting in ultra-low equivalent series inductance at high frequency. The coaxial capacitor array can be implemented in a coaxial cell of a power converter along with a coaxial semiconductor package and a coaxial inductor module for voltage conversion.