While thinking about new possibilites in Raid group combinations I tried a Phalanx Strength Spellbreaker Tank Build.
To the point: The trait Armored Attack in Defense does really weird stuff! You should gain 10% of your toughness as power but this is not working with half the stuff that gives toughness.
After exploring this further the following stuff gives the correct amount as far as I can tell:
Armor, Runes, Weapons, Trinkets, Bowl of Tropical Mousse (Toughness food) and the Grandmaster trait "Rousing Resilience" after stunbreaking, the firebrand skill "Epilogue: Unbroken Lines" works as well.
"Thick Skin" (base trait of Defense), Dolyak Signet, Banner of Defense, picking up an Earth Shield and the Guardian trait "Strength in Numbers", Halloween buff from Lump of Crystallized Nougat.
This makes a power based tank build worse than it already is, if the base trait and dolyak signet are both not giving the expected power buff...
I was not able to try out the Enhancement: Potion of Karka Toughness from Southsun Cove yet. Maybe I get back to that.