Transformer size

You can probably power them from the Z500, you won't be switching more than a couple at a time.  You can use a fixed voltage source as the switches won't mind, and the fixed voltage is cheaper and simpler.  I'd use #22 wire, no need for anything larger.

So, Gunrunner; If I understand you correctly, you're suggesting a single Z500 will handle all 12 switches with #22 wire, correct?

And, I'm not sure why you mention fixed voltage since I'm under the impression that both outputs of the Z transformers are fixed.

My experience is limited to the Z-1000.

It has 14 v available at the screw terminals and I thought the voltage available via the barrel connector might be slightly higher, although again, it's fixed -- perhaps 22v?

I assume the Z-500 is similar -- can you verify for me if the outputs of both Z-500 and Z-1000 are the same voltages.

I realize they will differ in the amount of current they can deliver (they might also differ in the voltage -- hence my question.)

Thanks

For 12 Realtrax switches, even a small 25-35 watt postwar transformer will work. You have a very low current demand.

The Z-1000 or Z-500 typically comes packaged with both the Z-controller and the brick.  If you just have the brick, you have a fixed voltage.  As Rob says, no real high power demands here.