Oscilloscope makes my mains (fuse box) group go down
Older equipment like this frequently has bypass capacitors connected between the wires of the power input, supposedly for noise reduction. There will frequently be one between Line and Ground and another between Neutral and Ground. These capacitors leak enough current to trip a modern GFCI &mdash; something that wasn't a concern back when the equipment was designed.

The fix is to open up the scope, find the capacitors, and disconnect them. If you're not comfortable doing this yourself, find a friend who has the necessary knowledge. One source of such a friend (if you don't already have one) would be a local "maker space" or "hacker space".