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Turns out it's 24 hours time since the Caps are depleted. Came back today and my Enclave had 200 cap reset. The others were left at 1, 2, 3, 4, 5 caps to identify faction.
Buying from vendors return 1/4 caps
Max cap a vendor can have is 200, so you should Sell before you start Buying
Cap stash is character based, not world/server based
Good strategy is to sell bulked junk that you are not using all at the same time to all vendors to max out 1000-1200 caps, so you have a reference as to when you can do it again the next day.
Edit: I've collaborated with others to fill the list and stopped doing my own research.