16BitBench has a crack at retro brighting with Sodium Percarbonate
I know this is going to be a contentious topic.
There are as many ways to do this as there are people who have have done it.
Some people swear against it saying it kills the plastic personally I think that's nonsense, you can certainly mess it up by using the wrong chemical or using to much. But at the end of the day this is just plastic stuff and as plastic stuff gets easier and easier to make through 3D printing and cheaper injection moulding then it's not really a tragedy if you loose a yellowed old computer case is it.
Anyway I've got off topic.
I'm going to show you something that works for me using Sodium Perconbonate and water to make Hydrogen Peroxide and on a sunny day takes only a few hours.