In my experience, kettlebells are by far the most suitable tool for highly specific exercises in order to increase power output in the key movements of a specific sport. Let's look at punching power.
Punching is a fast ballistic movement. The big kettlebells lifts (swing, clean, snatch, push-press, jerk) teach power generation through fast ballistic movement. No other training method does that nearly as well, except for Olympic weightlifting, but an Olympic bar can only be used in bilateral movements and Punching movements are not bilateral. Kettlebells can be used from a staggered stance and give themselves very well to unilateral and contra-lateral (rotational) movements, such as the ones found in boxing.
This video from Functional Patterns is just one great example of how Kettlebells can be used to improve body mechanics for specific movements like punching.
Key Benefits of Kettlebells in developing Punching Power:
Krav Maga Newcastle Coach Jeff Hollows runs Classes, Seminars and specialised workshops and is available for Personal Training in Krav Maga and performance enhancement specific to Combat Sports.