Sorry, I should have clarified. Assuming that turning on and off from the wall socket is what is wanted. If for example, I were to design and build a PSU, is it good practice / acceptable
To an extent that varies a lot from country to country. In general and in the case of a PSU; I'd have to say it is universally bad practice. In the case of the NEC I believe that it might not pass muster depending upon several factors. One question would be the proximity of the switch.
My NEC knowledge is rather old and frankly not up to date but in the past you had to have a local switch at the tool that was being used or some sort of overload protection for motor driven devices. This largely was applied to motor driven stationary tools as a running tool could overload and thus over heat. A power supply would or could have the same implied risk and devices like welders are required to have a local switch last I knew.
In any event if you forget the rules that apply for your area for a bit, I'd have ot ask why would you do this to yourself? Having a switch on a power supply would be the first thing I'd allocate panel space for.
to not include a device mounted on / off switch and just use the wall socket? Is there an electrical / technical reason why the wall switch should not be routinely used for this purpose?
Cheers
I can't think of a technical reason, I mean it could work, would it meet code requirements I don't know. However if safety and convenience are a factor in your life, a switch makes a lot of sense!