.To get the Electrobolt, you need to enter the Dark Aether and collect three energy crystals with your regular D.I.E. wonderweapon. These can be found at the following location and at any order. It is important to note, however, that you can grab only one crystal at the time, meaning that you have to make three trips to the Dark Aether in total:
At the roof of Nacht der Untoten, above the Stamin-up machine. There can be a Mayak guarding it. As soon as you picked up the crystal, the D.I.E. will colour orange and you shouldn't shoot anymore.
In the crashed plane area, near the entrance to the tunnel underground.
In the water pond, near the possible Mystery Box location and close to the entrance to the tunnel.
When picking up each crystal, return to the large Cyclotron room in the underground facility and shoot the crystal in the radiobox that can be found on the first floor of the room.
When you did this with all three crystals, you will receive the Electrobolt upgrade for the D.I.E.