[H] Six plus two equals eight?

[Winterlight]

I just bought a EVGA 1070 that I am installing. It has a eight hole 
power supply plug in. EVGA provide an adaptor that you plug two six 
hole plugs into and then plug that into the 1070 BUT the manual tells 
you that it is better to use a native power supply plug if possible. 
EVGA also manual points out that it is not the same as the 8 hole CPU 
power plug. Well, my Seasonic has a plug that has six holes PLUS a 
separate lead with two holes... is this what this plug is for?