klunkerbus
Getting the hang of it
By looking at the picture of circuit, it seems to me that the powerkit is a voltage regulator to allow continuing voltage to the DB1...
I actually had another paragraph in my post that I removed in a meager attempt to reduce the long post length. An advantage of shunting across the mechanical chime during the inactive state is that yes, the video doorbell will then be receiving pretty much the full AC voltage of the power transformer. The oscilloscope measurements in the earlier post confirm that (40vpp measured across the video doorbell, only 3vpp across the mechanical chime).
Without the shunt resistor, the available voltage will be split between the video doorbell and the mechanical chime, with the ratio driven by the load each device has. It won't necessarily be evenly split. It seems safe to say that not all mechanical chime coils are wound exactly the same, and the load from the video doorbell will vary - especially with IR lighting and audio speaking. Add in the variable of what any given transformer will output for that series load and you have quite a mix involved.