Does your Xbox spark and crackle when you plug the power cord in. If so you are one of the many Xbox owners who could be in danger of smoking your box and also a potential fire hazard on your hands. This tutorial will show you how to correct that problem if it is already going on or how to take pro-active measures to see that it doesn't happen or at least get bad enough to do some damage.
Follow the "How to open your Xbox" tutorial and get that baby opened up! Remember; make absolutely sure that you unplug your Xbox before opening the unit.
Now that you have it open remove the two screws that hold the power supply in place and slide it toward the front a bit and it will lift right out. Again, be careful because there are capacitors that store enough bang to make you jump or worse 
believe me... I know! Now flip that thing over and zoom in for a look.
Above is a photo of your average power supply, this one happens to be a foxlink.
See both tabs? The top one is obviously black and burnt but the lower one has also broken loose and is making intermittent contact.
A little alcohol and a q-tip to tidy up most of the vaporized lead
A little scraping with a blade removes the hard to get stuff
Dab a little flux and heat it up (800 degrees/30+ watt iron)
Be generous with the solder... Deliver the heat to the tab first and get it nice and warm,
then work the solder into the joint. If you fill under the tab until it flows over the whole tab
can get a pretty solid connection.
A quick touch up on the other contact and we are ready to rock and roll.
I like to squirt a little hot glue behind the A/C connector on the top side in the hopes that it helps
make it more solid. But, so far, I have had one fail again relatively shortly after the repair which
leads me to believe that it doesn't help much. If the pins are too loose and the cord is too tight
it will just break again no matter what you do!