I think that the most sensible approach would be some dice roll plus some fraction of max PP. Something like, say, 0.3*maxPP + 10d2. So if you have a PC with a max PP of 14 or less, it will always restore all of your PP. If you have a PC with a max PP of 50, it'll restore 10d2 + 0.3*50 = 25 to 35 PP, so half or a bit more. If you have a PC with a max PP of 200, it'll restore 70 to 80 PP, and if you have a PC with a max PP of 500, it'll restore 160 to 170 PP.

For an uncursed scroll, it could perhaps grant significantly less, like 0.1*maxPP + 8d2.

If that's a little too strong, perhaps the max PP part could be part of a dice roll... like, say, (maxPP/4+10)d2-maxPP/8, rather than 0.3*maxPP. This will produce a maximum PP boost of 3*maxPP/8 + 20 and a minimum PP boost of maxPP/8 + 10, with a high likelihood of it being approximately maxPP/4 + 15.

To give a sense of this, maxPP = 16 gives between 12 and 26 PP (so 12 to 16 with 16 being nearly guaranteed), maxPP = 64 gives between 18 and 44 PP, and maxPP = 256 gives between 42 and 116 PP. And similarly, uncursed scrolls could be similar but weaker. Alternatively, uncursed scrolls could work independent of maxPP, thus making blessing them an important step.

I think I like the idea. Grey is right. Even 160 PP isn't enough. It could still take 5 scrolls to get a full refill, and basically the only spell I've found that works in endgame is acid ball, which is expensive. If Bolt spells were actually good, then maybe 160 would be enough, but it's just not enough.

Scrolls of power now take fractional max power into account.

Does this change affect crystals of power?