Confused about powered risers and GPU power supply

[Spartan11]

Sorry this is very complicated to me, I greatly appreciate any guidance here.

I have a couple questions regarding a mining rig I am in the process of putting together.
First off, I have:
-EVGA 850 G2 (has 4 "VGA" outputs")
-Also bought Corsair rm850i (but I dont think this will work, I will explain later, I can return this if needed)
-MSI z170A krait gaming 3x motherboard (7 PCI slots, combination of PCI 3.0 slots: x16, x1, x1, x1, x8, x1, x4)
-GTX 1080 EVGA FTW (requires two 8 pins)
-GTX 1070 8 gb EVGA FTW (requires two 8 pins)
-GTX 1070 8 gb EVGA FTW (requires two 8 pins)
-Rx 580 8 gb Sapphire nitro (requires one 8 pin and one 6 pin)
-Rx 470 4 gb sapphire (requires one 6 pin)
-Rx 580 8 gb Powercolor (requires one 8 pin)
-I have several PCI 1x to 16x powered risers (right now I have 3 but I can order more)

First question:
1) I bought this dual PSU adapter, Raidmax 24 Pin 2 Way Dual PSU Adapter Cable - Control two PSUs with one button ATX Y Splitter (http://www.frys.com/product/8393337?source=google&gclid=Cj0KEQjw7dfKBRCdkKrvmfKtyeoBEiQAch0egThDFUS28vajucOei7enVnSfJR23hYwrSIXmaiXdfewaAiHQ8P8HAQ).
This thing does not fit into my EVGA PSU? My motherboard PSU slot currently has a an 18 pin and a 10 pin coming out of the PSU. The corsair PSU I also bought is set up the same way. Is there any sort of adapter I can use to use both PSU?
Alternatively, I can return the Corsair PSU and suck it up and just buy a 1200W PSU instead but this leads to my second question...

2) Any PSU I look up does not have nearly enough "VGA" ports ie the 8 pin PSU ports. Most of my cards require two 8 pin connections. Thats why I bought a second PSU in the first place. This does not even take into account the powered risers and what PSU ports I would use to power those.

3) Regarding powered risers, do I also need to provide power to the GPU via the VGA PSU ports? Ie if I have a powered riser hooked up via the molex cable, do I ALSO need to plug in the two 8 pin connectors if I put the 1080 or 1070 on the powered riser?

Thanks again if you read this far, I am new to this and really appreciate the help.

 

[Barty1884]

1. Combining PSUs is (extremely) rarely a good idea

2. Lots of PSUs have the appropriate connectors..... but you're looking at more expensive options, and higher wattage overall.
https://pcpartpicker.com/product/QG38TW/evga-power-supply-220gs1050v1
10 x 6+2 PCIe connectors.
You need 8 x 8pins and 2x 6 pins.
So, it has the appropriate PCIe connectors, just not enough power for your rig.

Your GPU power draw can be north of 1100W at max load
1080 = 180W
1070 = 215W
1070 = 215W
580 Nitro = 225W
470 = 120W
580 PC = 185W

Depending on the balance of your system, and to maintain decent efficiency levels.... you probably want 1500W+ from a single, quality PSU (incidentally, likely cheaper than the 2 PSUs you bought)

https://pcpartpicker.com/product/LbtWGX/evga-power-supply-220p21600x1

6x 6pin
9x 6+2pin

3. Yes, the molex power will only 'extend' the PCIe slot power, and the GPUs will require their PCIe connectors populated.

 

[ko888]

First question:
1) I bought this dual PSU adapter, Raidmax 24 Pin 2 Way Dual PSU Adapter Cable - Control two PSUs with one button ATX Y Splitter (http://www.frys.com/product/8393337?source=google&gclid=Cj0KEQjw7dfKBRCdkKrvmfKtyeoBEiQAch0egThDFUS28vajucOei7enVnSfJR23hYwrSIXmaiXdfewaAiHQ8P8HAQ).
This thing does not fit into my EVGA PSU? My motherboard PSU slot currently has a an 18 pin and a 10 pin coming out of the PSU. The corsair PSU I also bought is set up the same way. Is there any sort of adapter I can use to use both PSU?
Alternatively, I can return the Corsair PSU and suck it up and just buy a 1200W PSU instead but this leads to my second question...

You do not plug that adapter cable into the PSU's modular connector panel. You need to install the (10+18)-pin end of the cable into the PSU's modular connector panel and then plug the 24-pin ATX power connector end of the cable into one of the two adapter's input connectors.