Alien blaster

The Alien Blaster is a small energy weapon which appears in Fallout, Fallout 2 and Fallout 3.

Fallout and Fallout 2
A strange gun of obviously alien origin. Looks like it can support small energy cells, however.

Location
In Fallout, the Alien Blaster can be found only in the "UFO Crash" special encounter.

In Fallout 2, the Alien Blaster can only be bought from a merchant that you can meet during a random encounter north of Modoc.

In Fallout 3, the Alien Blaster is near by Powerplant 13 (up on map by way) (you can tune Alien radio SOS signal)

Fallout 3
In Fallout 3, the Alien Blaster can be obtained from the body of a dead alien lying a few feet away from his crashed spaceship. The spaceship is found northwest of Greener Pastures Disposal. It is not marked on the map. You'll know you're getting close when you pick up the "Recon Craft Theta" radio signal. The Alien Blaster uses unique ammo that is extremely hard to find. 120 shots can be found next to the spaceship. You can also find this rare ammo in Fort Independence, lower level, outcast weapons room. [Hard door]

There is also a random encounter that will trigger the falling of the blaster and ammo from the sky. It's location is variable and is preceeded by a green explosion in the sky, similar to a plasma weapon.

There is also some ammo located further west in the immediate area of the LPB broadcast tower to the west of the crash site

I've found additional ammo for the alien blaster infront of the grocery store Moira sends you to on the side quest about the Survival Guide. These alien power cells lie loose on the ground near the right entry door.