PLEASE, PLEASE, explain Lionel power supply functions

The TPC puts out zero watts, it's just a voltage controller.  Your ZW transformers are the only power source.  A post-war ZW is really good for around 200-220 watts of power at full throttle.  The 275W specification is for the input power, but there is conversion losses.

A transformer doesn't "put out" watts. The equipment the transformer is powering DRAWS whatever power (watts) it needs to run. Your old ZW transformer can DELIVER up to about 200 watts, but a single engine and a few cars won't DRAW that much.

Jerry,

As John stated the TPC300 is just a voltage controller.  It is controlled by the Cab 1/1L/2 handheld and varies the voltage received from the ZW to control conventional trains.  You do not need the TPC if you plan to control your conventional trains using the handles on the ZW.  All you need is the ZW and the Cab 1L:

If you want to control your conventional trains using the handheld, then it gets more complicated by adding the TPC300.  The maximum voltage the TPC300 will deliver will be equal to the maximum voltage set by the ZW.

Unless your layout is of good size and/or you plan to run a lot of conventional trains, I would not worry about the TPC.  I personally found controlling conventional trains directly from the ZW more satisfying than trying to use the handheld.  Note that I no longer run conventional.

make sure you run 14 gage wire around the whole layout.  two wires for each track.  run feeders off those wires every 6 feet using suitcase conectors.  i run my layout out with variacs and step down transformers.  old zw transformers will heat up if you run two trains on them alot has to do with amperage draw on them.  remember it is very important to run 14 gauge wire so you dont have voltage drops.

Thank you all, much appreciated, Jerry