An active-clamped isolated SEPIC DC-DC power converter (ACISC) to convert a DC voltage to supply a variety of DC loads. The single-ended primary-inductor converter (SEPIC) of the ACISC may be configured to perform both buck and boost converter functions. The ACISC of this disclosure may be configured to operate over a wide input voltage range to provide an output voltage for DC electronic loads supplied by the power converter. In the example of an automobile, a back-up twelve volt battery may output voltages to the ACISC over a wide voltage range, e.g., nine volts to eighteen volts. The wide input voltage range of the ACISC may be desirable when used as the converter for a back-up battery supply. The circuitry arrangement and component selection of the ACISC of this disclosure cause the power converter to operate in resonant DCM mode in the megahertz (MHz) frequency range.