the 18v does not come from the transformer, it comes from the driver board. you can follow the wire itself very easily down to the driver bd. I just don't recall which plug at this point.the 12v is done on the display p/s however It's only really used by certain brands of displays. I think you have a failed component possibly on each disp p/s and your new display needs it where as old display did not need the 12v. just a thought and I could be way off.