This is probably a dumb question or just my mind messing with me but can these two feats be used together?
Power attack only affects your base attack bonus. Weapon Finesse let's you use your Dexterity instead of your Strength to affect your hit chance. The two are compatible.
They maybe technically speaking, but it's sounds odd to allow. One is all about using force of strength to overwhelm your enemies and the other is about the substitution of strength to strike more accurately.