According to certain embodiments, an apparatus comprises port interfaces, charge storage devices, and a charge combiner coupled to a circuit board. Each charge storage device is associated with a port interface. Each port interface receives a current of charge from a device under test and pumps the charge to an associated charge storage device at a predetermined rate. Each charge storage device stores the charge from an associated port interface. The charge combiner combines the charge from the charge storage devices to yield a combined charge and feeds the combined charge to an output regulator.