A holdover circuit is configured with a holdover capacitor, preferably an aluminum electrolytic capacitor, to provide uninterruptible operation for an electrical load operable over a limited range of input voltage during brief power interruptions. The holdover circuit includes a switching regulator configured with two active switches that are controlled with complementary duty cycles to charge and discharge the holdover capacitor at a voltage higher than the voltage of the load. The controller for the switching regulator may be configured to regulate the voltage of the holdover capacitor at a voltage proportional to the load voltage or at a constant voltage. The controller for the switching regulator is configured to operate in different modes during normal powered operation and during holdover.