The power density of a single-phase ac-dc converter is often determined by the dc-link capacitance, which is sized to process the double line frequency ripple power. An Active Power Decoupling (APD) can help relax the requirements for dc-link capacitance by buffering the ripple power to an auxiliary capacitance. However, implementing feedback control of such a circuit typically requires either additional current sensing or complex control schemes. This paper proposes an APD strategy based on Extremum-Seeking Control (ESC), offering a simple, robust, and current-sensorless implementation that only relies on measurements of the dc-link voltage and grid voltage to compensate for the ripple power from the grid. This paper provides a detailed analysis demonstrating local convergence and offers practical design guidelines for implementation. Simulation and experimental results on a 5kW hardware prototype further validate the effectiveness of the proposed method in minimizing the dc-link voltage ripple.