I should really make a video on this as I have helped a few people accomplish this over the last few months.
I have a TI Keyboard version and I replaced the internal PSU, it is a pretty easy task if I am honest.
The PSU is a regular laptop type PSU as used on older Toshibas, Dells and IBM thinkpad type laptops. It also uses the same female connector to attach to the main TI circuit board.
Simply remove the keybed which once you have removed the screws on the bottom panel, eventually swings upwards - like lifting a laptop open - and the PSU is then visible. Take the old one out carefully, check the specs and grab a similarly spec'ed one off eBay where there are many to be found.
I don't come on here very often, catch me on facebook chat if you need more help.
theMouthPiece | RADIAS Demos | Cubase Studio 4 | Dell P4 2G RAM | Virus TI | Korg RADIAS | Korg KARMA | Absynth | Reason | KLC | Electribe EMX1 | Boss DR880