I've done exactly the same thing with my C128 power supply when it died. I replaced the internals with a switching 5V wall-wart and 9V transformer (both giving out more currency than the original was, and much lighter in weight). I arranged mine in V fashion so when you close the case everything fits tightly and do not rattle. I do not think that such PSU is more dangerous than the individual wall-wart itself and in my case it was the only solution since the switching chip in original PSU was dead and I could not find a replacement. I think the wall-warts have internal fuses and one could add additional fuses for output lines which would protect the wall-warts. I would not sell one commercially, but mine does its job well and has been in use for over a year.
