You mention Banjo signals. I have one - not controlled by a relay but merely by a button. I tried a DC transformer last year and, I can't remember which, but either the light didn't come on or the banjo didn't swing. Sorry that I don't remember but the point is that I had to run it on AC to get it to work.
I tried DC after reading so much about how accessories perform better with it. I've used AC for 30 years and it's always been OK, albeit noisy.
- walt