An external AC power adapter. The adapter includes a housing which, in one embodiment, defines an air inlet compartment, an air outlet compartment and a partially sealed electronics compartment containing electrical components for converting an AC input to a DC output. A blower generates an airflow within the electronics compartment for cooling the electrical components in the electronics compartment. Barriers are located in the air inlet compartment and the air outlet compartment to prevent liquid from entering the electronics compartment.