Power from an AC source at a source voltage is converted for delivery to a load at a DC load voltage, where the source voltage may vary between a high line voltage and a low line voltage in a normal operating range. DC-DC voltage transformation and isolation are provided in a first power conversion stage, the first stage having a CA input for receiving power from the source and a CA output for delivering a galvanically isolated unregulated AC adapter module (UAAM) voltage. First stage circuitry for performing the first power conversion stage is provided in a self-contained adapter module having input terminals for connection to the AC source and an output connected to the CA output for providing power to a second power conversion stage wherein the second power conversion stage is external to the adapter module.