I do have a question: when caroper mentions the (guesstimated) 500W, isn't that supposed to be the maximum the TX could handle? Or is that what it consumes regardless? I'm a bit confused (I need to read up on transformer theory)
Yeah, it's a max, they only draw it when you use it. (except for a little bit of inefficiency)
He's de-rating it because the wire was only spec'ed to handle a set amount of current.
It's a little more complicated than this but basically...
2000W/230V = Primary wire is intended for up to 8.7A
If you're now using this wire for 60V you can still only safely draw up to 8.7A.
So 60V * 8.7A = 522W
That said, transformers are normally pretty forgiving, you can push them more than other electrical components.
Especially if you're not running them continuously.
However, in this case, being from a microwave oven where it only runs for minutes at a time maybe they've already pushing it a little over spec