After completing Death From Above, talk to Tristan and he'll tell you about a new mission. This time, you'll have recover a Tesla Coil from an old Power Plant. Tristan tells you that you can enter the plant through the sewers in Olney. Once you find the entrance to the sewers, enter and you'll meet two ghouls. Talk to them and they'll run away. Now, proceed through the sewers, be careful though, there are lots of Deathclaws. Once you enter the Power Plant, make your way towards to the tesla chamber. If you need to, use the terminal to deactivate the nearby Sentry Bots. Once you have the Tesla Coil, return to Paladin Tristan.