"Power pulley" is a bigger crank pulley & longer belt(s) to fit that to slow down most to all things getting belt power for whatever jobs.
Covered in cave Watt Story w/ some common problem have this hype crap on a street car.
"Overrun / Decoupler" pulley in link just above
is not same thing!If this pulley is same size as OE pulley, does Nothing to Alt RPM.
If this pulley is Smaller then OE pulley, Speed Up the Alt RPM & very likely the Alt will Fail because spins faster all the time or even hit Alt's "Red Line" that mean hit or goes over Alt's max RPM that eats the bearings & more when bearing dies.
If this pulley is Bigger then OE pulley, Slows Down the Alt RPM & have same problems as "Power Pulley" causing Low Volts, Low Amps or both.
This is also covered in Watt Story.
Then why "Overrun / Decoupler" pulley... Simple to think like Shocks in car suspension that tries smoothing out impulse loads on a belt.
And Like Shocks/Struts will wear out & when does will have alt problems to start. More so making max amps as alt will behave has loose belt then pulley heats up & slips more or Fail completely. This is Part of Why almost no manufacturer puts this in a vehicle including Very High $ Models available to "the Public" to biggest trucks.
[This message has been edited by theogre (edited 06-29-2024).]