The Natural Philosopher wrote:

depending on current, a semiconductor soft switch or even variable speed
controller such as used for RC cars etc might be useful

Thanks. It's been suggested elsewhere (if I've understood correctly) that
it would be better to put an on/off switch (ideally with emergency stop) in
the main supply to the PSU and use that to control the lathe.

I had a vague recollection that it's ultimately damaging to a switched-mode
power supply to subject it to frequent turnings on and off, but perhaps I
was mistaken.