P.S. £20 = decent?
Not sure why you are waving the finger - a power supply that costs £20, is rated to do the job and turns a defunct PC from an ornament to a working system is fairly decent in my book.
Yes if you want seperate rails for different components for stability for example when using high end graphics cards you have to spend alot more.
But if you look at the power supply that comes as standard with just about all mass produced pc's you will see it matches the specification of the £20 dabs value replacement power supply I was reffering to.
It all depends whether you are comparing decent enough to do the job with excellent for the job.