A power-management integrated circuit (PMIC) is installed on a memory module to optimize power use among a collection of memory devices. The PMIC includes external power-supply nodes that receive relatively high and low supply voltages. Depending on availability, the PMIC uses one or both of these supply voltages to generate a managed supply voltage for powering the memory devices. The PMIC selects between operational modes for improved efficiency in dependence upon the availability of one or both externally provided supply voltages.