How many watts can wires in 6 pin to dual 8pin splitters handle?

[guacamayo]

I'm looking to power my next rigs with a server PSU instead of ATX style ones to save some $$$ and use 220V. My concern is with how I would power the GPUs. I have RX 570 (8pin power) and GTX 1070 Ti(8 and 6 pin).
I'm looking at PSUs like this one:
https://www.newegg.com/Product/Product.aspx?Item=9SIA8U258K3377
and a breakout board like this:
https://www.ebay.com/itm/New-Breakout-Board-10pcs-Cable-for-HP-1200w-750w-Power-Module-Mining-Ethereum/322886444267?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20160908110712%26meid%3De31e7eccddc64a128ff25ba41bdb4096%26pid%3D100677%26rk%3D3%26rkt%3D30%26sd%3D222589581252&_trksid=p2385738.c100677.m4598

(sorry about the link length). With an ATX PSU I can power the GTX 1070 Ti off of one 8pin slot in the PSU and the 8pin to dual 6+2 that it comes with. Would I be able to do this with a 6 pin to dual 8pin splitter? It's an 18 awg wire but from everything I've read, 6pin PCIe can handle 75W and 8pin can handle 150W. Does that apply to the breakout boards to the server PSU? I read up on as much as I could but couldn't find answers to how safe it is to say run on GPU (like a 1070Ti or 1080Ti) that requires two 6+2 connectors off a single 6pin PCIe connection on a server PSU breakout board.

Thanks for sharing your knowledge!

[1715359922]

1715359922

[MarkAz]

If I remember correctly the 6 pin is rated for 75w, and the 8 pin is rated for 150w - plus the card can also get 75w from the PCIe slot itself (or riser), so keep that in mind.  You've probably noticed that in many cases ATX PSU's don't even have the full 8 wires, just 6 and two ground jumpers to the last two pins on the 8-pin - this is because it's the gauge of the wire that're more critical to getting the extra 75w, not the extra pins of the connector (but they use them to indicate that the cable is higher gauge).

Generally speaking, you want to be careful about splitting PCIe connectors - while mining cables like the ones in the picture you sent are fine, but I like higher gauge (AWG) - 18AWG is ok, but 16AWG is ideal (although bother are higher than the ones you'll find on ATX power supplies).  There is also the max amount of power that the actual 6 or 8 pin PCIe molex connector can support (I may be off here, but I seem to recall it's around 225w).  The better plan is to go with a breakout that has more plugs on it - like I use Optimizer's boards with the DPS-2000BB, and it has 16 PCIe plugs on it.

Now that being said, splitting a miner-grade 16AWG 6-pin cable into two 6-pin's is going to be fine - consider a 16AWG cable might as well be an 8-pin - but I wouldn't split it into 2 8-pins or anything other than two 6-pins, or you're asking for trouble.  

[guacamayo]

That's a good note about the ATX PSU's, I hadn't noticed that, thanks.
It looks like I'll look into a splitter with 16 awg cable and use seperate pcie plugs if power a card with two power plugs. Thanks!