
Anauel |
Overhand chop makes the attack at 2x Str bonus instead of 1.5x Str bonus on a single attack, so yeah, it can be used with every feat that can be done with only 1 attack.
In this case:
Str 20 (+5)
Falchion 2d4 + 10 (2x Str) + 3 (2 handers normally do 1.5x, so Power Attack uses this).
So total, 2d4 + 13

Pirate |

Yar!
Power attack does not require a specific action, but is done as part of another action (attacking), thus you can power attack with most physical attacking options.
Power Attack when doing a Full Attack
Power Attack when using Combat Expertise while doing a Full Attack
Power Attack when doing a Whirlwind Attack
Power Attack when doing a Spring Attack
Power Attack when doing a Vital Strike
Power Attack when Charging
Power Attack when using the Attack Action (single standard action attack)
Power Attack when fighting with two Weapons
Power Attack when doing an Overhand Chop
Power Attack when Flurry-of-Blows-ing...
Etc...
Overhand Chop specifies that you must use a single attack via the attack action or a charge to gain the benefits. Thus, you can do a Power Attack Overhand Chop as a Standard Action, or you can even do a Charging Power Attack Overhand Chop (so long as you make only a single attack, as is specified in the ability)
Str 20 (+5)
Falchion 2d4 + 10 (2x Str) + 3 (2 handers normally do 1.5x, so Power Attack uses this).So total, 2d4 + 13
At level 3 with no other bonus from magic or an AA Whetstone, this is correct. Against object you also gain the Shattering Strike bonus you gained at 2nd level, making it 2d4+14 against objects.
~P
If you spend 15 minutes sharpening your blade with this whetstone, you gain a +1 bonus to damage on the next hit with that weapon. Does not work with magical blades.