Look what connectors you have on your cards 6pin-125W 8pin-150W then it will be easy to understand, as you did not specify what models you have. I would assume this PSU has at least 16AWG wires and uses all 8Pins/wires...
The cards, all use 1 8-pin connector, and I have two nitro+ rx570 that uses also an extra 6-pin but it says on the website its optional.