When I first read the OP I was surprised to read he needed 18 volts for the DZ-1000 machines when my DZ-1000s worked off the 14 volt fixed on a Z-1000 brick. Then I reread it and realized he was talking about a tinplate switch. Those switches (RossPlate) must have a lot more friction compared to the premiere or super lines.
Anyway, I believe each individual relay in the ASC2 is rated to 20 amps, so it should be able to handle even the higher voltages of the Z-4000 and post war transformers. As John stated, 18 volts would be no problem.