To remove yellow: ISO-Methil-ketone (don't know the english name).
Is that liquid yo momma/wife/girlfriens/sister/cousin (no offense) uses to clean out her nails.
Just rubs it with soft cottom in the yellowed plastic, then use some kind of neutral OIL to stop the ketone thing reaction, clean and "Hey, presto!", the yellowed goes away.
I do this on mine Miggy's cases to make palid/shiny white again.
Try on the original PSU first to see the results.