Mine was '80 certified' so yes they are definitely better. (little oval gold sticker with an 80 on it)
It's the same one found in the Gateway, Acer, HP, compaq in most instances.
Hell the HP we have downstairs from 2006 has a Bestec 350 watt in it and it's running an x800xl.
Not a hiccup yet.
If the machine works OK and you have no need to replace it then don't.
Just periodically clean the dust bunnies out from in and around the mobo and fans and you should be fine.