Toni: Sure, if you look at the more adcanced ones, and if you're willing to pay the price. However, just showing people how to use an ATX power supply on an Amiga bears the danger of someone taking some old PC's PSU, putting classic hardware in danger.
Kriz: As a result of the discussion on a1k.org, I'll look into designing a DC-DC converter that lets you use a standard 19V laptop supply for an A500/A1200.
Locutus: You're right, Meanwell makes good power supplies, but has recently changed technical data for some types that were interesting for the Amiga. Mind the wording: They *were* interesting, but are not any longer, as ripple voltage specifications were changed for the bad. I don't know the exact reason: They have either had complaints that the PSUs did not comply with the specs, or they have changed something in the design to make it cheaper.