Power Pistol will run more normal 38 Sprecial loads, and not-quite-full-magnum loads.
This ^^.
However, it may seem counter-intuitive, but you wanna run the 158's in the 38 Specials, and the 125's in the 357's. Power Pistol straddles the burn rate for potent 38's on one end, and not-quite-full-magnum on the other end.
Unique does this too, but not nearly as well, I think. Unique is known for its versatility, but it isn't as I define it. It does not run clean at lower (38 Spl) pressures and Power Pistol does (to a point, of course).
Those heavier 158's in 38 Special will keep the pressure up longer for a cleaner burn. The 125's for the 357 will get excellent velocity using Power Pistol without the big boom of 2400. Power Pistol is my go-to for 125's in 357; and I have all kinds of propellants from which to choose - including 2400. I reserve 2400 for full-throttle 158's in 357 (and 44 Mag for rifle - but that's another post). I don't like 2400 with 125's - way too boomy and flashy, with tons of superfluous recoil. Power Pistol does just fine - makes a very potent, excellent handling round. 1314 f/s through a 4" bbl - that's plenty o' poop, as far as I'm concerned.
All that rambling said however, I'd recommend either sticking with one or the other (loading 38's or 357's); or get more than one propellant. There's a lot of fun paper punching to be had with 38's using faster propellants. Good 38 Special ammo can be made using more conventional stuff like Bullseye, W231, AA#2, Titegroup, and others. These propellants sit right in the window where they run nice, consistent, and clean at 38 Special pressures. And using AA#2 and W231, I can get well over 900 f/s with 125's for my 38+P's - using published data - not hot-rodding. These are great rounds. Good little snappy recoil - truly fun to shoot.