Where are you located, what Country? If you are in the US it is assumed that you already have a transformer of adequate voltage but frequently users need a new transformer with 16V 30VA as the pro pulls a lot of power. If you are running both Pro Doorbells off the same transformer it is advised you get. 24V 40VA to support the added power draw. If you are in another country Ring sends you a Transformer as they assume that your existing system is not adequate. Ring Chime Pro has nothing to do with power required, it is an extension Chime and also a WiFi extender. If you are considering a Eero Mesh then you DO NOT need the Ring Chime Pro. One user mentioned using a wired back haul if you can run the cables, that is a far superior back haul over 5Ghz wireless. Wired Does Not lose signal strength due to distance or wall penetration signal lose.