What’s the green transformer about?
It's provided by the Utility to convert from high voltage (12.4kV typically) to 480V required by the superchargers.
is it always green or could it be inside one of the white cabinets?
I'm no expert by any means, but I think the green box is usually one of the last things to be installed before the SC is opened for business. There's often a wait for BC Hydro to do their work after the rest of the site is done.
Here's a recent example where the new Kamloops site just got their green transformer:
8 stalls coming soon to the Petro-Canada at 301 Southern Yellowhead Hwy, and it could be the first ever Supercharger built on native land in Canada!! https://www.kamloopsthisweek.com/local-news/tkemlups-looking-to-supercharge-its-way-into-2022-4542450 Article copied below: "Tk’emlúps te...