Yes, this is an extension kit. That means you connect the cables that came with your StraightPower to your power supply and then connect these extensions to the StraightPower cables. This way the cables get very long and you can get space problems in a compact case.

Cablemod also has cables that you can connect directly to your power supply. Here https://cablemod.com/compatibil... you can find the compatibility list. But as far as I know, Digitec doesn't sell all of them and the be quiet! cables are marked "discontinued".