I don't think the power supply is different from Mk to Mk on the SL-1200 series. I might be wrong. Also isn't the SL-1600 / 1700 / 1800 Mk2 electronics the same?
Both power supply board and transformer missing? There is a SL-1200 Mk2 power supply board for sale on organdonorparts. Maybe SL-1600 / 1700 / 1800 parts as well.
KAB makes an external power supply too. Not as $ as the Timestep.
I'm not up on the Timestep but considering that KAB and others do sell external PS and at least KAB doesn't sell different models for different Marks would, in my mind point to one original supply or at least supplies that could be swapped from model to model.