my psu is 500w with 6pin but 2 additional pins for an 8 pin
Did you open the case and confirm the brand and model of the installed PSU?
If the Aerocool is fitted, it has only one cable with a 6+2 pin plug. The GTX 970 needs one cable with a 6+2 pin plug and a second cable with a 6 pin plug. = two cables with two separate plugs.