As a bonus, with good form you won't break your hand.
There is no such thing as isometric wall punches.
Isometrics deals with a means to build muscle. To a martial artist, it typically means increasing strength at the ends of ranges of motion through stretching.
Martial artists do not strike walls, either. It damages both the hands as well as the structure, and achieves nothing.
The only thing that increases punching power is improving speed.
The only thing that increases speed are plyometric exercises.
(You can increase punch power by putting more mass behind the punch. But that slows the punch down, and unless you count pushing (distinctly different than punching) as a valid punch, you'd better have extraordinary muscle strength and mass to compensate for loss of speed.)
Don't punch walls.
Only 2 things increase punching power, or three, if by "power" we mean effective.
Technique is first. Nothing improves the "power" (ability to transfer energy into the target) more than improved technique. Second is speed. Faster hits harder than slower, simple as that.
Third (considering effectiveness as "powerful") is accuracy, the ability to transfer energy exactly where you want to.
If you need a tool, use a makiwara, which is far superior for learning how to punch than hitting a wall, or a bag. Use the proper tools to do the best job.
Well learn proper technique from there if you can't punch hard no problem, most people can't.
It's better to invest your time sparring or working on your technique, power will come naturally.
