I have several dozen Atlas switch machines, and I power them with a 12 volt ac power transformer from Radio Shack. It snaps em right over, and only cost about ten bucks.
IIRC, the Atlas swtch machines and snap relays are twin-coil devices. As such, they should have no problem with either AC or DC.
Some single-coil commercial relays specify DC only, but aren't polarity specific.
Chuck (Modeling Central Japan in September, 1964 - with twin-coil switch machines and some DC relays)
I think either one will work.
I am using atlas mark 7 switches and atlas snap relays to energize the frogs. Ihave a seperate trnsformer to op[erate thse switches do ai use the AC taps or theDC taps? Thanks,jimbon7