A few extra checks you might try to confirm the diagnosis:

Try a slow-blow fuse (if you aren't using them already). Transformers take what's called an an in-rush current when first powered which is higher than the normal running value.

Look at the capacitors. If any of them have a slight bulge in the end they should be replaced, though if one of them is faulty enough to blow that size of fuse then it would probably have detonated by now!

Disconnect all the transformer output connections making sure not to short any of the wires then try it.

You may have done all these, but buying a new transformer only to find the fault is still there would be no fun.