What is the infinite XP cheat on Fallout New Vegas?

Answer 1

This is more like a glitch to make it easier for the console users, but it still works in a short time:

You need Speech of 30 or the perk Confirmed Bachelor. You must also be on the good side of NCR. Go to HELIOS One and the lady should automatically talk to you. Once she allows you access HELIOS One, you should be able to start the mission "That Lucky Old Sun". Follow the mission and talk to Fantastic and Ignacio Rivas. While talking to Rivas make sure you get him to reveal that he's a Follower of the Apocalypse by using Speech or Confirmed Bachelor and agree with his ideals about peace or just say you're neutral. Do the mission regularly until you get to the point where you activate the Mainframe Terminal. Configure the Power Grid to "5) Full Region (Emergency Output Level). Finish the mission by hitting the Reflector Control Panel outside on top of the tower. Go back to Ignacio Rivas and choose the option "I overloaded the plant. No one.....". The glitch is that the option never disappears, so you can choose to keep pressing it. You get 350XP, 3 Stimpacks, and 2 Doctor's Bag