If a supernormal power can be used to attack a foe, the GM must determine the strength of the Power for damage purposes preferably during character creation. An offensive Power is usually handled as a propelled weapon, such as a gun, or as being equivalent to a certain melee weapon. This can just be expressed in terms of damage, though, such as Ball of Fire, +6 damage, or large Claws, +3 damage. (See Sample Wound Factors List).
In the case of a magical or superhero attack, the more potent the attack, the greater the power required, or perhaps the greater the strain on the character who uses it. This can be a penalty to the skill level, greater fatigue, and/or some other disadvantage.