The RING has an internal lithium battery and charging circuit. Is it possible that the RING requires a specific range of current draw that the external resistor provides (20vac/25 ohm = 0.8A). I spoke to RING tech support and they are clueless. Also this resistor will draw 16W continuously 24x7... a doorbell chime only uses power when the button is pressed. Isn't this a bit weird?
Oh good point, for some reason I was thinking there was still a N/O switch in the loop, but that is of course on the Ring unit itself..
Now it makes a bit more sense. When the resistor is installed, you can't have the diode as well or too much DC current would flow continuously.
What I'm thinking still is there is a small high resistance transformer inside the Ring unit, and it shorts that out to run more current through the chime and actuate it.
So it is possible that the unit may not draw the full 16W (you could measure it), and it only requires that resistor to prevent too much current flow when the internal transformer is shorted. The unit may be too "dumb" to know if there is a series chime installed or not, so resistor is a simple fix. The resistor value is not necessarily determining how much current is flowing, only the maximum.
The fact that they spec a 50W resistor is a bit scary though.