I have an old case that takes a PSU at the top.
I bought a PSU made for being at the bottom, and placing it in their meant giving it the CPU heat in its intake. It felt like it would burn up any minute.

I took some used aluminium cans, cut them up using expensive scissors (~5x the price of normal scissors, in turn, it won't go bad, cutting plastic boxes and aluminium sheet) and made a frame to mount the PSU on the top, instead of inside the case.

The wires had to go around, making it a partially open case, but it worked. No feeling of imminent fire hazard and the PSU was exhausting air at a relieving temperature.