The capacitor suggestion in the link would look like this:
The idea is the 25-cent capacitors smooth the pulsing DC voltage that follow the diodes. I did not get from the discussion if someone actually tried this. But from a technical perspective, I'd think this method has some details to work out. With your existing diode method and 16V AC supply, the switch motors receive a voltage of about 12V DC. By adding capacitors of a size that would effect meaningful smoothing, the voltage the Tortoises would see would jump up to 16V DC or more. The voltage would depend on how many of your 20+ switch motors were "straight" vs. "diverge". I think I read somewhere you don't want to apply more than 12V DC to these motors(?). If you pursue this option, I'd install 12V DC regulator electronics after the capacitors to generate solid/smooth +12V DC and -12V DC. There are eBay voltage regulator modules where you could do this for less than $5.
The last post in the link thread suggests 2 DC supplies connected in series. This is the method 2 from the Tortoise instructions.
For example, this could be 2 12V DC wall-warts. Suitable wall-warts that can power dozens of Tortoises are about $2 on eBay (free shipping from Asia). I'd suggest a pair of 50-cent screw-terminal adapters to simplify wiring so you don't have to splice into the coaxial barrel plugs.
Obviously you need access to a pair of wall-outlets. If this is a show-stopper and you want to use your existing 16V AC source then the diode method augmented by capacitors and the like can be further detailed.
I'm ignorant as to your 2nd question.
