Diode rectifiers charge the reservoir or filter capacitor to the peakvalue of ac as well as supply the load's power demands. However, as the ac wave drops to 0 V, load power actually comes from energy stored in the reservoir capacitor. As energy is used, the output voltage of the capacitor droops, reducing the average voltage available to the load. The amount of droop is independent of voltage. Instead it rises with load and drops with capacitor size.