A question for catalyst centre
what is the function of power control , what would happen if +20 power or -20 power ,will the fps change ,or other things ? I want to know it in detail .
I'm sure someone else will be able to better explain it, but here goes
Power control allows the user to define how much power(Watts) the graphics card can draw, so say for example you wanted to overclock your graphics card you'd want to allow the card to draw as much power as it needed, otherwise the overclock may not be stable (You'd have to provide the card with enough power to maintain stability).
You may want to use -20% if you want to reduce how much power the card uses (Save on energy slightly, uses less power so less heat and noise...).
There's many people that have asked a similar question to your's so if my explanation isn't detailed enough there are plenty of threads and articles on the subject via a quick google search.