18 gauge on that psu.

18awg are good enough.  Each wire can carry 15Amps at 2Ft.  That's 180W per cable.  However the connector 6pin or 8 pin has a max current of 7(or 8) Amps per pin.  It's not the wire that you worry about but the connector.  

As a licensed electrician since '73, you guys are promoting BAD & WRONG info.
Here is an industry standard chart that explains PROPER current for 18 & 16 AWG : https://www.engineeringto...wire-gauges-d_419.html

We electricians use the NEC code book in North America & we have a site that we login to with our license info which I can't share here but the site I posted is for both AC/DC & if you want 12VDC specifically then drop down on that page & it brings you here: https://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html
 
We are NOT authorized to rely on manufacturers data else we lose our license for life. We are instructed to only utilize our NEC codebooks. Back in the early days, an apprentice wired a friends home with 14/2 AWG NMD90 for their 15 AMP wall outlets which was correct & legal but then he used the same 14/2  for their 20 AMP outlets which was illegal because he was supposed to use 12/2 & because the house caught on fire due to his work he lost his license permanently. Larger wire gauge size (thicker which means smaller AWG #) has less voltage drop & sustains more current & propagates less heat through the system due to less resistance of the thicker wire.

 

phantomshroom
We electricians use the NEC code book in North America & we have a site that we login to with our license info which I can't share here but the site I posted is for both AC/DC & if you want 12VDC specifically then drop down on that page & it brings you here: https://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html
 
We are NOT authorized to rely on manufacturers data else we lose our license for life. We are instructed to only utilize our NEC codebooks. Back in the early days, an apprentice wired a friends home with 14/2 AWG NMD90 for their 15 AMP wall outlets which was correct & legal but then he used the same 14/2  for their 20 AMP outlets which was illegal because he was supposed to use 12/2 & because the house caught on fire due to his work he lost his license permanently. Larger wire gauge size (thicker which means smaller AWG #) has less voltage drop & sustains more current & propagates less heat through the system due to less resistance of the thicker wire.

 
yes, I've use the NFPA 70®: National Electrical Code® before, many times professionally
 
 
 
The load is only 6-8 Amps per pin - by design --> seems you are missing that little fact
 
For clarity:  My EVGA 1200 Watt GPUs use 18 GA AWM wire .. and run 24/7 ... no issue after years of heave use
 
 
Yep, those breakers are not a safety device if the wire is glowing before they trip.
 
That apprentice - is luck they did not go to jail or get sued all the way to the poor house ...

phantomshroom
Solid wires (NO CORES) are more resistant to corrosion & can sustain much higher current than stranded & have less resistance & voltage drops than stranded which helps produce LESS heat in the cables than stranded ...

I feel like you didn't read what I wrote.  Also, the illustration you provided purposely exaggerates your point.  Your illustration exaggerates the gaps and reduces the strand count to only 8.  The chart you linked to goes up to 43 strands, but the number it gives for "43 and above" "cores" seems way wrong.
 
As I stated, I agree when talking about low strand counts, but as the strand count increases, the size of the gaps in the cross-section become smaller and smaller, and the benefits of surface area (skin-effect) more than offsets any losses due to the small gaps in the cross-section.  In essence, it is a process of comparison of area versus surface area.  A high number of strands has high surface area and only a small reduction in area.  A high number of strands is better at conducting electricity than a single strand.
  
This is what your chart looks like:

 
This is what it should look like:

 
At 43 (and more) strands, I would expect it to be way beyond the point that an upward swing is evident.
 
 
 
And to be fair, none of this is very relevant.  As said by Epal2Apol, at either 18 gauge or 16 gauge, the current limitation is the connector pins themselves; by a significant amount.

No one disagrees that larger GA wire (physically larger diameter conductor - smaller GA number) can carry more current with less voltage drop ... we are talking <30 Inches not 100 feet
 
See link:  https://www.evga.com/support/faq/FAQdetails.aspx?faqid=59690
 
850 Watt to 1300 Watt (13 Amps models) .... use a 16 AWG cord from the wall to the PSU .....that cord is 5 to 6 feet long
 
So why would you - NEED 16 GA individual wires - for the gang sockets - on the DC side ?
 
Economics is Second only to safety .... larger is better to the point where there is no reasonable benefit
 
 
 
1300 W /120V = ~ 11 Amps ..... wall power cord is rated @ 13 Amps .... you want all the cords to be 12 AWG ... "because it is better"
 
Do you wire all your 15 Amp circuits in a home with 12/2 or better yet 10/2 because its better than 14/2 ?  
 
After all a circuit in a home can be well over 100 feet in length .... of course not --> economics says ---> you do not exceed the minimum required safety standard as required by law