Thanks Bob. I woudn't have posted at all except for the fact that I was busy writing mine when yours popped up. I tried to emphasize simplicity and provide a reference, which I had to look up. (I can't get away with posting ex cathedra, as you can. ) Of course, "my" source supports your scheme at least equally to mine; and better if you add accessories.
What I failed to mention was that the opening paragraph of the source that I cited gives a better-than-nothing overview of the concept of "common ground" which I thought might be of general interest to the forum. Given the precise nature of the original question (at least as I read it) and the fact that its was the questioner's third try, I deliberately chose to eliminate all consideration of adding fixed-voltage accessories. In the end, your choice of options is more versatile.
One thing that neither of us pointed out was that the metal plate on top of the transformer likely shows all that really needs to be known -- if it's still legible -- right under the throttle pointer, showing the hook up posts for the two throttle ranges: AU high; BU low. It's amazing how many folks never see this; or, if they do, don't understand what it means. It is a feature common to many old Lionel transformers.
If I recall correctly, you employ an old Type Z (as opposed to ZW) transformer. One feature thereof is a max voltage output of 25 or so, which some pre-war trains might need. Or does the fact that most of the wall sockets now put out about 120 volts, as opposed to the 110 volts that were common in "the old days" mean that the "19" volts of the high range on the Type RW will actually measure in the low twenties, and be more than enough? (I'm not certain that was a sentence, but it was meant to be a question.)
Related questions are what do see as the normal house voltage at your wall sockets; and what is the max no-load voltage you can get out of your Type Z? Thanks in advance.