Note that this question is not a hardware recommendation. The actual PSU and server case quoted in this question are given merely as an illustration; the question itself, as it was explicitly specified since the beginning, applies to any ATX PSU (and naturally any 2U server case).
Power supply units which are made specifically for servers:
Are often very expensive, especially Gold and Platinum variants,
Have features that ordinary PSUs don't have, such as redundancy,
Are rarely modular (I suppose),
Are poorly documented (how many P8/P4 connectors do they have? How many SATA/SAS disks can I connect?),
Are usually (very) noisy.
For my particular need, I would like to purchase a 2U server chassis, but use a PSU I already have, Corsair HX1000i, which is a non-server PSU.
The documentation of the server chassis is very sparse and not very helpful when it comes to the list of compatible PSUs:
PSU Form Factor 2U Single or 1+1 Redundant
When comparing the size of Corsair HX1000i to two 1U UPS devices, it looks like the PSU has the same height plus one to two millimeters; this is scary, because I could imagine that it might not enter inside a 2U case. The height of the PSU is 3.39 inches, while 2U is 3.5 inches—barely a 0.11 inch difference.
Is any ATX PSU compatible with a 2U server chassis?
Do I have to care about the side of the PSU where the fan is (see the photo above) being blocked by the top panel of the server chassis?