A portable, pluggable power line communications device provides convenient interfacing and connectivity between separate data networks interconnected over the same conventional electric power conveying media. The power line communications device plugs into a single electrical outlet, and includes a controller that is programmable at the device or remotely. Remote programming is achieved over the same power media to which the communications device is coupled, or by wireless link. The power line communications device controls data communications signal transfer over the common electric wiring of a local network, and conducts high-speed communications and download of multimedia signals from an upstream network controllers using the common electric power media. The data communications signals of the co-existing, different networks are encoded to permit differentiation at the power line communications device.