A good place to do this is at the "F.O.B. Armadillo" enemy base in the Itacua province (where the game begins). This is an Unidad controlled military base in the east with a power generator. First, buy the C4 skill from the pause menu. Once you have it, enter the base and throw C4 at the generator. Blow it up to get the "Black-out Boomer" achievement. The generator also respawns every time you fast travel. Thus, it is not a problem if you previously destroyed it. Just fast travel there again for it to respawn.