There are so many great exercises that enhance punching power. Squat jumps for example will make your punches more powerful. The power of a punch is generated from the legs. In fact, the biomechanics of the punch begin with the muscles in your feet (off the ball of your foot) firing through the calf and then up through the leg as the hip rotates from the pivot. That power gains momentum as the torso rotates until the arm finally delivers it. Stronger biceps and pecs have little to do with punch power. I do not want to exclude the importance of muscle balance, but like most sports- your legs and core carry more responsibility for generating power.
Often when I teach a punch, I reference golf and baseball. First of all it helps me to explain why the dominant arm goes in back instead of in front. This is especially valuable for those that come from traditional martial arts or play sports on both sides. When you think about trying to knock a ball out of the park, you have to have the timing to connect, but you have to drive power from the ground like the horsepower you get from a two-stroke motorcycle.
This concept is not difficult for people to understand. But it is hard for people to understand how to connect the legs pivoting, the torso rotating and arm extending in synchronicity. This exercise with an adjustable head cable machine is fantastic for heightening this muscle awareness, understanding how to keep the upper and lower body connected when throwing a punch and is very sport-specific. I hope you enjoy it. It can be done as reps and sets or in rounds of time (30, 60,90 seconds). I suggest starting with light weight so you do not compromise your form.