If the card consumes less power than others, a single 8pin is sufficient. Other cards probably have the option of raising the power limit, which consumes more power, and in return you get an additional 6pin.

That is not quite correct. The GTX 1080 consumes a standard 180 watts, so an 8-pin connection is sufficient.
That is also enough for a little OC. I run mine at a stable 1950 Mhz with a minimal increase in the power target, and there's not much more to be gained with an additional 6-pin, air-cooling systems achieve a maximum of 2050-2100 Mhz on average.

I see. Then the chipset alone is not decisive, or despite the same chipset, the power consumption of the different models is very different... I wasn't aware of that. Thanks for the information.