Tom, one size fits all for the TVS, the same one will work for AC or DC, I use this one: 1500W 33.3V TVS at Digikey. There's no reason you can run AC on one line and DC on another line, just as long as they don't actually end up being connected together. You can also run PS/3 stuff on DC, and if it's all PS/3, it doesn't care about polarity. PS/2 runs on DC, but PS/2 does get picky about polarity.
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