This is a plugin for Details! addon, you can't use it standalone, if you doesn't have Details! installed, download through this link click here or curse client.
How to use: While in a raid group, open a new window of Details! clicking on the new instance button or typing /details new. Choose "Raid (plugins)" at gear menu and after that on sword menu choose "Raid Power Bars".
Alternative power bar are the special power bars present on specified encounters like The Stone Guard on Mogu'shan Vaults, Norushen on Siege or Orgrimmar and others.
For any issue with this plugin, please open a Ticket at the Details! Bug Tracker, here: http://wow.curseforge.com/addons/details/tickets/ Thank you!