A single-phase, single-stage, isolated active-clamped SEPIC PFC converter with a partial power processing (PPP) output stage is presented. The PPP stage is implemented with an extra winding in the isolation transformer, low voltage rating diode and MOSFET and a series coupling capacitor. This converter features zero-voltage switching (ZVS) for the main switch and the clamp switch in the main power stage, and zero- current switching (ZCS) for the auxiliary switch in the PPP stage. The output PPP stage enables output voltage regulation, double line frequency ripple cancellation and fast dynamic response for the output voltage. The double line frequency ripple in the output voltage is reduced significantly with the PPP stage, which translates into significant output filter capacitance reduction and power density improvement for the single-phase PFC converter. The performance of the proposed converter is verified with experimental results.