would a MCRU LDA linear power supply work with the MDAC2, or is the new PSU a whole different topology/connector?
The MCRU unit, and the similar Swagman,are only "3-rail" supplies, like my home-assembled dual Calex supply, and connect via the original 9-way DIN connector on the back panel. Fancier versions ( see my comment above about 5- rail supplies) have to work with the outer sleeve removed, and some dangling wires (see Miterdog's "plydac" pictures a week or so back).
John commented earlier that the PS input to the MDAC-2 is a D- connector, "to make it easier for Home builders" (maybe not his exact words) to connect on their own supplies, but I think this means at least a "5-rail" supply. You and I are in the same position- when we get the MDAC-2, all we can do is entrust our old supplies to the mercy of e-Bay.