Actually I've been sort of looking at ML computers (kind of of browsing and dreaming one day I would have one, but it's always going to be out of my means and needs anyway). Anyway, they can put two PSUs in a box, obviously it's made by companies, so the total cost is twice or 3 times the cost of the parts alone (e.g. building yourself would be 2-3x cheaper) but it could inspire you for picking your parts.https://bizon-tech.com/amd-ryzen-threadripper-up-to-64-cores-workstation-pc

https://shop.lambdalabs.com/gpu-workstations/vector/customize