“Each level of Action Boy/Girl gives you an additional AP to spend every combat turn. You can use these generic APs on any task.”— Fallout 2 In-game description
In Fallout and Fallout 2, the counter only shows up to 10 Action Points, but internally keeps track of any extras. In Fallout Tactics all APs are shown properly.
In Fallout 2, if Agility is an odd number, it is more advantageous to take Gain Agility before or instead of taking Action Boy/Girl, as the former will confer an additional action point as well as the other benefits of higher Agility.
“With the Action Boy perk, you gain an additional 25 Action Points to use in V.A.T.S.”— In-game description
The Action Boy/Action Girl perk grants an additional 25 Action Points to use in V.A.T.S. This is sometimes used as a substitute for a high Agility rating, and is helpful for characters who rely on V.A.T.S. rather than real-time combat.
The Action Boy/Action Girl perk grants an additional 15 Action Points to use in V.A.T.S. mode. Compared to the Fallout 3 version of this perk, it awards 10 fewer action points per rank, but two ranks exist instead of one.