There is no event ATTRIBUTE_VISUAL_INCREASED_REGEN_POWER or EVENT_ATTRIBUTE_VISUAL_INCREASED_REGEN_POWER
It is a constant value:
ATTRIBUTE_VISUAL_INCREASED_REGEN_POWER = 3
http://wiki.esoui.com/Globals#UnitAttributeVisual
Some more info please!
What is your usecase, what did you expect and what is not working?