Don't know about the reduced power spring, but I tried to put a Wolff "factory strength" spring in a new 686 and it hits the rebound slide when cocking it in single action.
I emailed Wolff technical support about it and they said it would need a longer strain screw in a 686. So I just put the factory spring back in and left well enough alone.
The Wolff spring did seem to be a bit smoother, so you might like it, if you want to be bothered with hunting up a screw and fitting it.