PCjr questions and TI 99/4A tidbit

Hello! I have a working PCjr without any add ons to it. All It had is two types of keyboard one is clicklet and one is real keyboard, parallel sidecar, extra 64k in it totals 128k and a 5.25" But it is missing a power transformer, it uses dual tapped 17vac connected to one tap inside the transformer making total of three wires. But I made up a power adapter to accept clone pc standard switching PSU in place of its little AC to DC convertor card. One time I booted it with 5.x dos but I had to set video mode to arrive at 80 columns at end of boot. Is the orignal transformer brick underpowered if I put extra add ons? Is that true that there is a lots of add ons for this PCjr? I would like to seperate the video to a proper video such as VGA card so it would not hog up the main memory and boost it to 640k. Finally is there a add on that allows me to plug a DMA chip in to speed up the floppy? It is nice compact computer! What I planning is to make this PCjr more of an real XT with SLOTS than a just a cheap vanilla-favored PCjr. Where's is good source to find these parts? Oh, by the way, my father still have a TI 99/4A in black/sliver case with all the stuff but not the expansion box. It is bit iffy and joysticks is worn out from lot of use by me and my brother. Both of us would program in lots of basic and see what it does. SLow. :) And both of us would play the Peaseac I think a LOT. What's is the best way to retore it to an reliable one again? Thanks!