Question....if someone has a damage bonus of +8, then adds +5 from Power Attack, how does that affect someone with Protection +10? Does the Protection negate the weapon? Or does he make a regular damage save vs. +3?
The damage bonus from Power Attack is not affected by the stacking limit (which affects powers, not feats) and is included as part of the damage bonus for determining whether or not a target with Protection needs to make a Damage save.
(In other words, Dr. Obvious and AaronUnicorn are quite correct.)