To obtain powerups you need to take over 'Rally Points'. To take over rally points you need to manoeuvre your Rally Troop over the rally point and wait until your troops have descended on the rally point and sacrificed themselves on it. After enough time and sacrifices the rally point will be yours along with the powerup that it offers.
You can unlock this during a quick match and have a second controller connected to make this achievement extremely easy.
Obtain 50 powerups by taking over 50 rally points and the achievement is yours.