Sharing some of the experiences I had dealing with power on my TZ, in case helpful.
TZ has unregulated 12V (aka ~15-17V on my machine) and regulated 12V. You'll want regulated 12V for fans.
I've switched out the 12V regulator in my TZ (and all my WPC games) with a modern switching regulator, which was a huge help with stability (12V is used for switches among other things):
https://www.ezsbc.com/product/psu3-12/
If you're pulling your power board, upgrade the 5V supply to a modern part as well (-> no more CPU resets):
https://www.ezsbc.com/product/psu5-nonoise/
Countless gremlins went away for me after these power upgrades. Both run cool to the touch and no longer require heat sinks. That is a good thing on electronics getting close to 30(!) years old.
Even with that, I ended up putting a computer power supply in my TZ, and run 12V/5V/3.3V from that for all/most of the mods I have hanging off the machine. Peace of mind when trying to track down issues, and I'm a big fan of off loading as much as I can from the vintage electronics.
I just received some RC motor coolers off Ali Express yesterday. I'll be installing this weekend and playing with them. Wasn't planning on dropping them in my TZ, but your experience with fading has me curious.
