Cell2Jack runs on a 5V USB power adapter, the same kind that charges a cell phone. You almost certainly already have a spare one, which is why the box shares power instead of adding another adapter to a drawer full of them.

Which adapter to use

Use the 5V adapter that came with your cell phone. Cheap aftermarket adapters can add a hum or buzz to your calls. If your audio has noise, the adapter is the first thing to change. See bad or noisy audio.

The 5V out port

Cell2Jack also has a 5V out port. You can run your cell phone charging cable from it to keep your cell phone charged while it sits nearby. This is optional.

Connection diagram The home phone cord runs to the Phone port on Cell2Jack. The power adapter short USB cable runs to the 5V in port. Below the device, a dotted Bluetooth link connects to your cell phone. No wire runs between the cell phone and Cell2Jack. Home phonePower adaptershort USB cablePhone5V in5V outCELL2JACKBluetooth, no wireYour cell phone
The home phone connects straight to Cell2Jack. The wall jack comes later, after pairing works.