or you can try to replace or re-route the transformer to have more stepping down.
i think replacing a psu as a whole would be the easiest & safest way
ps i don't think all 220v is 50hz & frequency doesn't matter because afaik, the dc voltages supplied to the ps2 are generated by dc-dc conversion & regulated through voltage regulator. because whether it's 50 or 60hz, it will be same once converted to dc through w-bridge.
i am an expert, so someone knows about this stuff should exam the psu, but i am pretty sure.
Ref +: psaras, marcus21, sirusxXx, gamecubesuxs