Striking power, like throwing speed (baseball for example) is very highly genetic. It can be improved, but not as much as other skills.
Assuming that someone has sufficient foundational strength, the key is high-speed work. Medicine ball throws (single hand, both hands, etc.) works well, but ideally with a lighter ball with maximal speed. Power jerks, power snatches, light push presses or DB push presses can also be beneficial.
One could even do overspeed work.
In my experience, overspeed work is the best way to improve speed-dependant skills. it consists of doing the skill itself, with more speed than you can normally use.
For example, in golf you have golf “clubs” with a weight instead of thre clubhead. The weight and aerodynamics of these trianing clubs allow you to reach a swing speed that can be 10-15 mph faster than a swing speed with the driver. By training on that you are teaching the nervous system to do the movement faster and over time it will increase the speed of the “real” movement.
Overspeed training too my golf swing (with driver) from 112mph up to 124mph.
My friend, and former client, Stefan Jones also does a lot of overspeed work with cricket bowlers to improve their throwing speed.
How can you do that with striking? You can use bands. Essentially attach a band to a post in front of you. Grab the band with your punching hand, walk back (you still want a small amount of band tension when the arm is fully extended at the end of a punch). Load for the punch (which will streth the band). And then punch as explosively as you can. The stretched band will make you punch faster than you can, normally.
I recommend sets of 3 punches, focusing on quality. And ideally you complex that with 3 regular punches in the heavy bag (to get the best transfer possible). Do 3 overspeed punches, rest 2 minutes, 3 normal punches as hard as you can.
I like to start with 3-6 sets per side.
Rotational and anti-rotation work is fundation work. It will not improve punching power i itself, unless you are severely deficient in core strength. BUT it can be useful in that it will keep you more stable under overspeed conditions, allowing your body to use all of its speed potential rather than instincitvely put the breaks on to avoid an injury.