Yes, it can be converted from 120V to 220V and vice versa (been there, done that).
If I recall correctly, there is a thick jumper wire inside the PSU soldered to 120V through-hole pin/via which has to be removed for 220V.
Thank you Hese for your tip . My friend and I successfully turned my new beautiful A3000D's PSU 120V into 220V
It really is that simple as you described, although was scary when it came to turn it on for the first time (with the mobo disconnected of course so in case something went wrong only the PSU would smoke, but still...). But it nicely started on the European voltage and all measures on the big plug were correct. Then connected to the Amiga itself powered it up showing wonderful kickstart welcome picture (and now working with two hard drives and loaded with fancy cards)
Here are some photos taken before and after the whole "operation":
And here's fully assembled (do not mind crappy un-configured Workbench) and with a small addition showing the internal temperature:
Haha classic! Sorry for that!
It's a friend of mine in US (Rod Whitney) who attracted my attention onto that as I told him it was very easy to convert by just cutting a wire... He said, hold on... No! Haha.