6-pin Connector

I recently bought a “SATA 8-Inch 15-Pin to 6-Pin PCI Express Card Power Cable” so I could plug my new 1060ti graphics card into my pc. The problem is I can’t find anything to plug the 15-pin side into. I have an Inspirion 3668 dell and the only other upgrade i’ve made to it was a cpu upgrade...

So I've bought Gigabyte 3060Ti Gaming OC Pro, but didn't noted that it comes with extra 6-pin PCI-e connector compared to non-Pro version. Problem is I have older PSU that comes only with single 6+2 PCI-e connector, which if possible I would rather avoid to replace. PSU in question is Chieftec...