Hi Kimbo123,
Weight lifting is good supplemental training but the primary constituents of punching power are genetics and proper technique. So, if you're looking to improve your punching power to your highest potential, perfect your form/technical execution first and adhere to the "law of specificity," which in simplistic terms is directly/exactly practicing and training (which are two different things by the way) the shit out of what you directly/exactly want to improve. In other words, if you want to be good and powerful at punching, don't try to improve it through swimming, tennis, and/or anything else unrelated to your objective; simply punch more, conscientiously emphasizing functional power in the process. One excellent way of doing this is by repeatedly hitting a dense heavy bag with single shots, emphasizing optimal body mechanics with each and every deliberate shot.

One last thing, continue lifting weights but do so knowing that it's a supplement to your sportive training. By the way, do you know what the primary benefit of weight training is? Well, its main function is to strengthen your muscles, tendons, ligaments, and bones, which help to reduce the likelihood of injury through improved musculoskeletal integrity. With that, it indirectly/secondarily helps improve athletic performance because you're able to work out harder, faster, and longer as a result. So, keep that in mind.

Anyway, hope this helps...

Take Care,
Lito