powertune allows you to manually override the max power draw by the card if needed.
It won't make any different if the actual power draw is below the factory settings, which is usually the case unless you overclock the GPU a lot (the GPU takes most of the power, not the RAM), or you overvolt the card to a certain point.
Mine is currently set to '-20',what does this mean?
Every card has a maximum amount of power that it will draw. PowerTune can adjust that number up or down.
PowerTune of 0 is the factory default. Setting it to -20 means the card will dynamically adjust it's clocks to keep the power draw 20% lower than the factory. +20 gives it 20% more power.
I keep mine set to +20. It doesn't mean it's always using 20% more power, but it means it's capable of using more power when needed.
