The sweet science comes down to much more than just punching power, but to understand boxing on a scientific level punch power is a good way to start. If a boxer wants a win via knockout then they're gonna want to have some heavy hands, some bombers, the haymakers. This can be understood as simply as the equation for force, because the more force behind a punch (with the right accuracy) will achieve a knockout. Force equals mass times acceleration.
It's no secret that heavier weight classes punch harder, because they have more mass. That's why you see guys like Francis Ngannou and Derrick Lewis being the top 2 hardest hitters in UFC. They've actually measured these guys punching power and Francis Ngannou holds the world record for most powerful punch at 129,161 units of force.
We measure force in newtons. So to punch harder you need a solid amount of muscle mass. Then you need the technique that comes with it. The speed and ability to throw your body mass into the punch, which is called a "kinetic chain". The average amateur boxer is hitting around 2,500 newtons of force and striking contact with about 300 pounds of force per hit. Ngannou and other heavy hitters are striking at well over 1,000 pounds of force per punch.
Your punches are kinetic energy and equal the mass of your body to the fist, multiplied by how fast it's moving between point A (somewhere beside you) to B (someone's face.) That momentum making contact and transferring kinetic energy if your punch. Kick, elbow, headbutt, whatever.
Force = Mass X acceleration
(punch power) = Fist / Body behind it x Speed from A to B