What does power kit for doorbell pro do?

If I can get it to do color again (another thread) I intend to gift my original ring doorbell to a neighbor and replace mine with an already purchased doorbell pro. My current doorbell is supposedly running off power, not battery. Is it really necessary to install this "pro power kit" on my doorbell? Or can I just replace the outside unit with the pro? What does the kit do? Is it just the optional diode that came with the original? I did not need that diode.