WPA4220T is power line adapter, also called power line range extender.

All TP-LINK power line adapters can work together.:cool:

Method 1: If you have NOT used the pair button to pair up the current units, just plug the new unit and wait 1~2 minutes. Then the 3 units will work together.
Method 2: If you have used the pair button to pair up the current units, plug the new unit and press its pair button, then press the pair button on either of the current unit (but don't press both). Wait 1~2 minutes. Then the 3 units will work together.

But remember only the models started with TL-WPA or TL-PA are power line adapters.
Don't mistake them with Wi-Fi range extender TL-WA850RE/TL-WA860RE/RE200

Thanks for the reply. So, for example a TL-PA451 (AV500) pass through unit is compatible with the WPA4220T (AV500) network?

Yes

Magic, many thanks radvd.:)