Power to The People stations will allow you to get upgrades to each of your weapons, the further you go into the story the more weapons you will have and the more upgrades available.
There are only a total of 14 stations that can be found here
You will have to both upgrades for the same weapon before it will give you access to the third one get this achievement.
e.g. Drill upgrade rank 1, 2 and 3
Tip for you.
If you are have already purchased 2upgrades for one of your weapons, but you would really like to upgrade a different weapon rather than spend the ADAM, save the game, purchase 3rd upgrade of the weapon.
Unlock achievement, then reload.
You get to keep the achievement and you can also upgrade something else instead