Nice to see one more Spanish Amiga user around.
dfreniche, I've been using an A500 on an A1200 for years, mine was one of those heavy and old A500 PSU, fully reliable. Another option is to use a PC PSU, you can easily adapt one following this instructions:
http://aminet.net/package.php?package=hard/hack/ExtraPower.lhaYou'll only need the original Amiga PSU plug.
BTW, check your PM.
Saluditos,
Ferrán.