EXPLOSIVE POWER - sounds like a sudden blast of TNT or in boxing - the ability to change pace suddenly and score effective punches with knockout potential. so we have two key issues - 1/ learning to suddenly change speed from neutral to high speed, and 2/ learning effective punching skills
Learning how to shift your weight properly is I think the easiest way to make your hands heavier. Start actively thinking about throwing your bodyweight into punches and you'll see results. Well I did, anyhow.
To me, i always think about explosive power as projecting your full bodyweight into a target as fast as possible. When i train especially on the heavybag, i try to make my punches as "dynamic" as possible and incorporate my entire body into the technique, whilst trying to avoid as much wasted movement and energy as possible. In a sense, im not "hitting" my target/opponent per se, im "slashing" at it, attempting to chop it down. Sorry if that doesn't make sense. There are many ways outthere to train explosive power, but personally i found that explosive power just came as i got more proficient with the techniques.