New build with recycled parts on a ridiculous budget 120cm*60cm work area

[Neale]

Would wiring a 5amp plug fuse to the PSU input give some protection to without tripping out in normal usage?

I suspect that 5A might be a bit small and might blow on switch-on, although you will probably get away with it. Typically, a standard fuse will blow within 10sec with a 2x overload, so that might be OK. For normal running, you are unlikely to be drawing anything like 1000VA (which is a touch over 4A in practice) most of the time, if ever, so that's well within the fuse rating. I use a 10A MCB on my own machine feeding all the PSUs (although the stepper driver PSU is the most power-hungry) and I haven't had it trip yet.

Unfortunately, the fuse is very unlikely to protect the equipment and that's not really why it's there. In practice, the fuse blows just after the equipment fails! It's really there so that in the event of a serious fault that draws excess current, the wiring isn't going to burst into flames. In the case of elecronic components, it's well-known that the transistor is the fastest fuse on three legs...