Funny you mention that. I've noticed my punch isn't as strong on my "away" workouts either. I think it's a matter of road stress, poor rest/diet, and the ergonomics of the equipment. Not all benches are the same angle, width or length; even different dumbbells throw me off. You're just not as relaxed at an "away" gym. You don't have the comfort of knowing the people and location of all the equipment.
Proper nutrition by planning meals ahead of time will help.