The name brand boxes may use a different wiring schema. However, there's only one connector involved, the 20/24 pin motherboard one. The wires are colour coded so you should quite easily find out if the wiring is different to standard. I was going to say you could reassemble the wiring but it's not too easy. It's doable based on what I've heard but you might end up pulling the cords off the connectors as I did with my testing sample. So you'd better just check before buying.
Of the two the Dell looks much more worth the price. Also, Intel has a better reputation being compatible with AH, AMD used to have issues in using more than one core. Can't tell if that should be true with that one, though. Further, the HD7770 uses at least as much power as the 1060 you're planning to get so the original power supply should do if the connectors allow for it.