External power supplies are standalone units that convert AC (alternating current) from the mains electricity to a lower DC (direct current) voltage required by the electronic device. They are physically separate from the device they power and are connected via a power cable. Examples include wall adapters, phone chargers, and similar devices. Internal power supplies are integrated within the device they power but are considered off-board in the sense that they are not part of the main circuit board that performs the device’s primary functions. They still convert AC to DC internally and distribute the power to various components within the device. The choice between external and internal (off-board) power supplies depends on the specific requirements of the device, including considerations of size, heat management, and maintenance.