I can recommend the FSP Group FSP400-60APN 400W PSU, it has low ripple values on the 5v line and is a cheep PSU, 13-19mV ripple between 25-100% load on the 5v line is quite good, great value for it's money 
The problem with this PSU is that it only provides 15A on the 5V rail, which may be a bit low if the Amiga has a floppy drive, harddisk, CD-ROM and other stuff connected.
Personally I use a Antec Basiq BP500U in my towerized A1200, and this PSU can provide up to 30A on the 5V rail. It might seem a bit overkill, but then again I do have a Apollo 1240, Mediator, Voodoo GFX card and various other PCI cards installed there.
