A direct current (DC)-DC converter, which includes an open loop ripple cancellation circuit, a switching supply, and a parallel amplifier, is disclosed. During a calibration mode, the parallel amplifier provides a parallel amplifier output current to regulate a power supply output voltage based on a calibration setpoint. The switching supply drives the parallel amplifier output current toward zero using a switching control signal, such that during the calibration mode, an estimate of a current gain is based on the switching control signal. Further, during the calibration mode, the open loop ripple cancellation circuit is disabled. During a normal operation mode, the open loop ripple cancellation circuit provides a ripple cancellation current, which is based on the estimate of the current gain.