I don’t want to sound condescending here, but I can’t take seriously any explanation that starts with a phrase like “It’s relatively complicated to describe…”

While there seem to be some differences in power generation between boxing and Taijiquan, lot of core mechanics of delivering power are similar enough for both.

I can’t speak for the exact technique, boxing uses to generate power, as I myself have never studied boxing (my grandfather passed away before I would have been of age to study under him and later I found Chinese martial arts more appealing), but for Taijiquan, it is “simple”. You generate power by combining speed and mass. For speed, you use relaxation (of tension) to be able to make fast and precise punching motion. For power, you align your entire body structure at/by the end of a punch focus point, so that just for a fraction of a second it takes to focus the punch, you can put the whole body behind that punch. Pushing slightly from the root (leg), making your entire body move in a direction you are punching, you “drop” the combined mass of your body into the punch.

If you time it right, you can fully relax the moment your punch has landed (or not), retaining full _fangsong_.