I'm not sure what you mean by "older", but the Realtrax and Scaletrax ITADs I've seen can be powered by DC or AC.
I have dis-assembled and drawn and posted schematics of the MTH ITADs on OGR for the common good. If you have some oddball application such as powering the ITAD with DC but need to switch AC - or whatever - I can probably help you out.