The PS5503US is a special AC Power Adapter. It can be used to power either 1 or 2 interface units. The PS5503US adapts 120V AC to 9V DC (500mA). It offers a built-in 50ft cable with bare wires, allowing it to be easily connected to the interface or line driver. The PS5503US may also be used with other DA1900 Series products that require a 9V 500mA power adapter.