You can just supply power from a standard AC transformer. Note that without a command base, they'll power up in conventional mode, and you won't be able to test most of the functions. Obviously, you'd probably want a variable transformer, not a brick. For proper function testing, you will also need a TMCC or Legacy command base connected.
I took some 3/4" plywood and spare Fastrack components, I cobbled together this stand. The two level design is so I can put the locomotive on test rollers and have the tender on the elevated section at the right height to connect the wireless drawbar. This allows me to do full function testing.
In the middle of the lower section is an uncoupling/operating track section for testing those functions of operating cars.
Each section has a pilot light and a power switch so I can enable disable the lower and upper sections independently.
The power input is standard banana plugs, and I have a switch to isolate the outside rails so I can test 2-rail stuff on the stand as well.
