Anyone know if it’s safe to wire my MRC Throttle Pack 027 AC transformer (or any modern “electronic” transformers) “in-phase” with other post-war transformers? Safe for the transformer, that is.
If not, how do I deal with trains passing between blocks controlled by two different transformers when their wheels are touching both blocks’ outside rails?
For years, I used an MRC Tech II Trainpower O27 and Lionel 40W (1990’s - probably a 6-12885?) together, in-phase, exactly for block control on my “under tree” (Christmas) layout.
I remember cutting a notch in one side of the plastic plug on the un-polarized MRC power cord… (the intention was to mark the side matching the longer spade of a polarized plug so that I could keep them in phase when re-plugging them in - but if I had a nickle for every time I forgot what my marking meant… 
Anyway, my setup gave me several holiday seasons of trouble free operations!
Good luck with yours !