Hi der_fisherman, guten abend.

I've parked this problem for now until I've finished off some house DIY jobs, and can also finish off the mechanics of the CNC machine. I'm sure you know how it is!

But when I'm back on this again I can do the checks you suggest above, although as I mentioned if I run the board from DC instead of the AC supply everything is fine. Roy's CNC board products have a good reputation and following, so I'd hope he know about handling the parallel port properly.

On the suspected faulty power supply front because it was 2 years since purchase I'm understandibly on my own with that one, although it did have this problem from new but had ignored it. That leaves me with:
Making my own linear supply (with Irving's and John's help above) - had the figure of ~£55 for that option, plus my labour
Purchasing a switched mode replacement unit from Roy ~£60 (but sending it back for a refund or replacement if it glitches)
Purchasing a lower spec (but exactly the same make) unit from China at 27v instead of 32v for ~£40

As for Windows SP etc, I've tried it with a fresh install of Linux running EMC2 and it still glitched.