The displayed damage is the regular damage. Power attacks do extra.
The Nukapedia page on Melee Damage states that
- Melee and Unarmed attacks in V.A.T.S. do twice as much normal damage, but this doubling is done before Strength is added.
- Power attacks in real-time combat also double normal damage.
The damage was doubled in previous Fallout games, but the Damage Resistance page says that, for close combat damage in Fallout 4,
PowerAttackMulti = 1.5
So it's possible the multiplier may have changed. Regardless of the multiplier, power attacks do more damage, rather than normal attacks doing less.