Lets Talk Wiring And EMI

No problems at all. I did my fair share of such installations with the difference that I did that on working computers, so it was all in a single box, although to much wires.
The only empty ones I used were a small shuttle PC and had the same PC so they looked nice together, still do after nearly 5 years with a lot of dust on them. The other empty one used for some time ( it is empty again in the workshop waiting patiently ) is an Apple G4 that I gutted to use the box for electronic. It was in perfect working order, just had a slight issue of drawing nearly 600W of power to work. That was to much since my other PC at that time did 450W and was twice as fast.

The amount of interference produced by HF/HV start plasma and TIG as they use the same thing is impressive , but it is very hard to explain to people who do not deal with it as it can not be seen.
Proper grounding is a must, shielding on cables also, but sometimes just changing the mouse or the keyboard will do the trick nicely. Until recently I could find used Dell or HP or IBM keyboards and mouses and they were very good, especially the IBM ones as they are the best keyboards to type on, but they are getting hard to find, so now I tend to use Genius or Logitech, and also found some very cheap ones with proper shielding that work with plasma, they were 4 euro a piece and got 3 of them, now I can not find them anymore.
Also USB extension cables can cause issues, find transparent ones so the shielding can be seen, also found one such type that looks properly shielded but caused issues and after checking with DVM it turns out the shielding was not connected to any of the connectors !
Oh and please no roled up wires/cables, that might look good, but it is terrible for collecting interference .

Internet if full of .... well everything.
As a result of that, there are plenty of info regarding electronics stuff from good to plain dangerous and utterly stupid.
It does not matter what type of power supply you use, switch mode is cheaper and easier to work with and much lighter in weight ( for a machine not important at all ), all that matters is:
-DO NOT ever buy a 50V power supply for drives that have 50V written on them, the cheap ones will just blow the instant you turn them on. Always leave 10 to 20% margin under the max declared voltage. There is a huge difference between "absolute maximum ratings" and normal working rating for electronics, cheap ones have that absolute rating written on them.
-Get the most powerful one you can afford and forget about the "internet math" that if you have 3 drives at 5A you need a 15A power supply, you don't never ever need that. As a general rule, half of that is a very safe value for any power supply over 24V ( yes yes the current drawn is very dependant on the voltage provided, more voltage=less current, so at 60 to 70V you could get away with just 5A supply and everything would work just fine. Note that there are very few drives that can handle that kind of voltage and they are not cheap )
As for the above example i made with laptop power bricks, if you have to ask for an example, do not go that route. Any miss wiring will result in lots of smoke and/or bodily harm, as intentionally removing grounding is not a good idea.
Since this might make it more difficult for you to decide, her are some safe values:
24 to 36V at 10 to 15A SMPS is enough for 90% of use cases. At 30 to 50$ there is nothing cheaper. I use the above mentioned solution as i can not find anything above 12V here, and i get the used laptop bricks for 10 to 15 euro a piece, so for me it is a very nice solution.