Why do people ociate the confederate flag with 'white power' type groups?

Because it's a representation of the OLD SOUTHERN way of thinking (that blacks were worth nothing and should still be slaves). The Southern whites from the Confederate states flew this as their flag during and after the Civil War. They still had their horrible ideas that a free black slave was trouble and lazy and that they did no more than take all the good land from the whites. The KKK was given free reign to go and terrorize the blacks when they felt like it and they were the epitome of those screaming "white power". You can be sure they had their Confederate flags waving proudly. The Confederacy wanted to keep whites in power and wanted nothing for blacks other than chattel slavery; the flag was a tangible symbol that they had seceded from the Union. Even though they lost, they still believed blacks deserved no rights. That's why, to this day, the Confederate flag is stated to be one of the symbols of white supremacy.