I dont know about exercise dude..

The only thing i could recomend.. Practice correct technique.. Ive had help with tecnique of punches in the past and it helps greatly..Especially the jab..

Of course bieng strong and bieng muscular etc is going to help when you hit someone.. But for the sake of punches like a jab..Where if you just throw it without snapping it out its really just an arm flung into your face.. A large poke.. Its much easyer to get power into shots like your strait right and left hook..Because you put body weight into it..You turn into a left hook with your hips.. put the shoulder and bodyweight into your strait right..And both can be stepped in with from your back foot..Sort of applying your weight better.. If thats the right way to describe it.. But the best thing you can really do is really understand how to throw your punches down to a tee and practice till it becomes the norm..
Hope this is of some help to you.. You got a trainer or anything? take you through your stuff help out etc?.. Hope its not patronising if you are experianced or something i just dont know so jus giving what advice i can think might help
Peace