A portable medical device includes an interface for accepting a power supply and enabling data transfer while still connected to a human body. The interface may include a universal serial bus interface and may be coupled to a data isolation chip and a power isolation chip. A power controlling processor may determine how the supplied power, e.g., voltage, is supplied to other components within the infusion device. Additional circuitry within the system may provide a secure power transfer within the device to ensure user safety and ensure that a high frequency noise is properly attenuated.