nVIDIA and AMD/ATI are the source for the actual GPU chips on the cards. The other manufacturers, however, will produce cards with their own (usually proprietary) cooling solutions, or other details that set them apart (more/faster VRAM, more HDMI/DisplayPort jacks, OC'd/UC'd in comparison to the reference GPU, etc.).
So....if the item is listed just as "nViDIA GTX 650 Ti", then it's a "reference" card (i.e. card manufactured 100% by nVidia). If it's listed as "ZOTAC nVIDIA GTX 650 Ti", then that means nVIDIA provided the GPU chip, but ZOTAC built the rest of the card, & may have made other changes (slight OC out of the box, extra VRAM, extra DisplayPort jack, etc.).