you dont turn over a punch to create power you turn it over to connect with the last three knuckles. you connect with this part of the fist because they are the knuckles that are above the wrist and when you connect with the last three knuckles the fist and the wrist will "lock" together. jack dempsey called it the power line. its an invisible line running through the arm extending out of the last three knuckles and through a target. dempsey said that the last three knuckles stabilizes the power line, but the power is coming from the entire process of creating the power line and sending it through the arm and out of the fist, not from the fist. i think that hand strength contributes to power but only by contributing to how stabilized the entire power line through the arm is making the power more "locked" at the points in the arm, such as the wrist, that are designed to bend and therefore lose stability in that area and weakening the power line and therefore power. i dont think hand size is power. julian jackson had small hands and thin arms.
arm punches arent as heavy as true punches but they can be hurtful. foreman is the famous arm puncher, but he turned over all his punches and always drove his punches, and therefore the power line, all the way through you. the check hook is an arm punch, but still devastating for these same reasons. most of all, because its a counter punch, it represents the most overlooked aspect of punching power, which is actually shock. i think the most powerful punch is not the punch that is the heaviest or fastest, but the punch that is more than any other attribute, the most shocking.
, the average person will need to use their shoulders and hips for power punches. Just like some cats are heavy handed, George Foreman and GGG comes to mind, and they don't rely on their hips, shoulders or legs. To each his own I guess.
At all promotional companies using the same 12 year old RJJ photo. 
, it should be announced soon