This 48V-12V DC-DC converter handles 10A, pretty sweet, only $17. This will give me a massive regulated 12V supply off the machine's existing massive 48V switcher, which will power the Smoothieboard and any outboard stuff such as the vacuum handling.

Smoothieboard also needs 5V, which by default it gets from USB but I prefer a standalone supply so for that I will be using a small DC-DC switcher that can do +5V at 2A from 12V.