That is right, it is a 6+2 connector intended for use where 8 pin connector is called for. However, Apevia is one of the worst possible PSU brands you can buy. That 1000w unit is completely unlikely to be able to supply anything like that except maybe for a second or two, if that.
There are NO professional reviews of this unit, unlike ANY other unit of halfway decent quality has. When there are none, you can bet it's because it's a crap unit. AND, that's before already knowing that Apevia has a long history of being horrific in quality. Might as well have just taken your money and lit in on fire in the dumpster as buy one of those power supplies.
I almost never refer to Amazon or Newegg reviews, because they are practically never accurate at all. Usually, if the item arrives at all, it gets a good review. In this case though, even on Amazon, fully half of the units have failed or have not been able to supply even half of the rated wattage.
https://www.amazon.com/Apevia-ATX-JP1000W-Certified-Performance-Crossfire/dp/B01IE0C8WU
Plus, I have about six hundred links to threads where Apevia power supplies were the SOLE cause of a variety of system issues, most of which were related to the graphics card.
http://www.tomshardware.com/answers/id-1964719/power-supply-failure.html
http://www.tomshardware.com/answers/id-3776091/thermaltake-smart-series-psu-question.html
And this review of an Apevia 900w unit on JonnyGuru that received probably the worst score of any power supply ever reviewed there.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story4&reid=92
Bottom line, get a quality power supply FIRST, and then go from there. Until then there is little point in even trying to diagnose anything as it's a waste of time.
Your RX 460 only calls for 380w, with the whole system included. The GTX 1070 on the other hand, calls for a recommendation of 500w minimum, which is a 120w difference and likely exceeds what your power supply is able to muster up. Might even be possible that the PEG connector has a problem using those other two pins on your 6+2. Now, I'm not saying that it CAN'T be something else causing your issue, because it could be. But it's practically pointless to try and figure it out when we already know you have a terrible, horrible and extremely bad, no good example of a power supply to start with. Unfortunately, that's not even an exaggeration.
I don't know what country you reside in, and I know that sometimes it's hard to come by good units in some regions, but when possible, when it comes time to get that PSU, I'd stick to the following if you can.
Seasonic. Just about anything made by Seasonic is good quality for the most part. There are really no bad Seasonic units and only a very few that are even somewhat mediocre.
Corsair. The CX and CXm units are ok as a budget option, but I do not recommend pairing them with gaming cards. The newer 2017 models of CX and CXm are better than the older ones, so if it specifically says 2017 model, then it's likely at least better than those older ones. Aside from that, any of the TX, RMx, RMi, HX, HXi, AX or AXi units are good. Those are listed from best to worst, with the best being the AX and AXi units.
Antec. The True power classic units are made by Seasonic, and are very good, but are not modular. The High current gamer 520w and 620w, or any other PSU you see on the market that is 520w or 620w, are also made by Seasonic, based on the S12II and M12II platform for modern versions, and are pretty good units but they are an older platform that is group regulated so if you go with a Haswell or newer Intel configuration you will want to avoid those because they do not support the C6/C7 Intel low power states.
They CAN be used, if you turn off C6/C7 in the bios, but I'd really recommend a newer platform whenever possible. Prices are usually pretty good on those though, so sometimes it's worth accepting the lack of DC-DC on the internal platform. Higher capacity versions of the High current gamer are not based on that platform, so they are fine. Those being the 750w and higher versions. Antec Edge units are ok too, but reviews indicate that they have noisy fan profiles.
Super Flower. They are like Seasonic and they make power supplies for a variety of other companies, like EVGA. Super Flower units are usually pretty good. I'd stick to the Leadex, Leadex II and Golden Green models.
EVGA. They have good and bad. Bad are the W1, N1, B1, B3 and G1 NEX models. Good models are the B2, G2, G2L, G3, GQ, P2 and T2 models.
FSP. They used to be very mediocre, and are a PSU manufacturer like Seasonic and Super Flower, although not as well trusted based on historical performance. Currently the FSP Hydro G and Hydro X units are pretty good.
I would avoid Thermaltake and Cooler Master. They do have a few good units, but most of the models they sell are either poor or mediocre, and the ones they have that ARE good are usually way overpriced.
Beyond that, there is a pretty good basic guideline available at the following link, although it has not been updated with newer models in about a year.
And most of the models I have linked to the reviews of at the following link are exemplary.
http://www.tomshardware.com/forum/id-3612443/power-supply-discussion-thread.html
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