@amiga40001
My Amiga 4000 also uses an ATX PSU, and I have never had any problems with it yet, other than user related problems :-D
I think it is a 450 watt, and it powers an Amiga 4000, CyberStormPPC 060@50 604e@233, ELBOX Zorro II/III busboard, Mediator PCI 4000, Voodoo 3 3000, FastEthernet, Terratec 512i soundcard, TV card, Algor USB, 1 x 160 GB hdd, 2 x CD-RW and 3 IDE --> SCSI bridges.