Sorry, I forgot about the last question in your post!
In my experience, fitting a new
PSU is relatively easy, just open the case, unplug all connectors from the motherboard, hard drive, DVD ROM etc then unscrew the 4 screws holding the
PSU in the back of the case, and gently remove.
In all my cases I have never had a trouble removing it because of components being in the way, but maybe some do depending on the cases?
Then it's as simple as screwing the new one in the case and connecting up all the connectors again! You cant really go wrong, you would know if you were trying to fit a connector in a socket that it didn't belong in!
Thats my 2 cents anyhoo!
Smokeycheech