OK sorry it took so long to respond, I was at work.
The PSU I am using is a
Solid Gear Flex 320 Watt Mini-ITX Non-Modular Power SupplyThe form factor is a FLEX-ATX which is a derivative of the MINI-ITX form factor.
This PSU is 6" x 3.25" x 1.6" so it is pretty small. Much smaller than the original 3000 PSU. (But far more powerful)
https://www.microcenter.com/product/457426/solid-gear-flex-320-watt-mini-itx-non-modular-power-supply?storeid=029A few considerations when swapping the PSU on a 3000 is that the power button is built into the PSU so when using a replacement you need to replace this functionality.
If you purchase the adapter from Amigakit, this switch is included with it.
Also due to the smaller size, you will need to customize things a bit to secure the PSU in your case. (I am printing off a custom bracket for this purpose)
I have x2 3000 machines, one with a 68060 CPU and the other has a 68040. The 060 runs pretty cool, but the 040 is a smoldering beast so I have also printed a custom part that holds a blower fan that mounts where the 2nd floppy drive would mount.
I cut a hole in the PSU / Drive mounting plate that sits above the CPU card exposing the CPU. The blower sits above the CPU (with an installed heat sink) and pulls the air from inside the case over the CPU and thru the heatsink and then is exhausted out the front of the case. It is too loud as I used one of those slot type blower fans I had laying around but I don't care at this point. It works very well and keeps the 040 very cool and that is all I care for the moment. Someday I will redo it and maybe install a rheostat to control the speed but this does the job for now.