GPU Power Draw Distribution

[TowerSales]

So I'm currently attempting to upgrade a Dell pre-built with a new GPU, specifically an Inspiron 5675 which shipped with an R3 1200 and an RX 560. I have already replaced the CPU with an R5 1600x and installed a solid state boot drive. My GPU of choice - which I've already purchased  - is the MSI RX 5600 XT Gaming X. I made this decision based on its good power consumption and performance figured in comparison to other 5600 XTs, as well as the fact that until recently it was priced attractively in my region. The problem I am anticipating is with the PSU, even though the 5600 XT has modest power requirements and my 460W Dell PSU (eww, I know) does exceed the recommended 450W power requirements on the MSI website - for some reason the Gaming X uses two 8-pin power connectors. This is for a card with a 150W TDP and an (empirical) power consumption under load of 120W. My PSU only has a single 6+2 pin connector, and Dell used to ship this PSU with RX 580s which draw more power than a 5600XT, using just that single 8-pin. At this point I am seriously considering using some sort of PSU adapter (eww, again I know) - so to summarise my question is this:

 

Is there a way to determine which of the 8-pin inputs the GPU will draw from first, so that I can make sure that one uses the actual PCI-E power cable, or would the power draw be distributed evenly?

 

Here is the main source I used to make this decision:

 

[boggy77]

i would just get a new psu and don't trust the one that comes in a pre-built dell that was made for office work.

[Ralf]

The problem with that psu and adapters are that's it's 3 rail psu. 12VA=18A, 12VB=16A, 12VC=8A and max combined wattage is 385W, you would need to find out which rails go where so that you dont overload them.

[GDRRiley]

5 minutes ago, boggy77 said:

i would just get a new psu and don't trust the one that comes in a pre-built dell that was made for office work.

its a gaming desktop that had up to a 1700x and 580 or 1060

the card looks like it can peak at almost 200W in furmark but should only hit 150W which a single 8 pin is fine with MSI is weird

 

 

[TowerSales]

12 minutes ago, boggy77 said:

i would just get a new psu and don't trust the one that comes in a pre-built dell that was made for office work.

You see that was my first instinct of course, the only problems being the inflated PSU prices at the moment, and the fact that while the PSU is ATX in terms of dimensions and mounting, Dell in their infinite greed decided to design their case so that it is impossible to install an ATX PSU with an external power switch without first snipping through plastic. That, and the fact that Dell used to ship these PSU's to power RX 580's and R7 1700x's, kind of led me to believe it might not be as bad an idea as it sounds.

[TowerSales]

Ye that's basically what my research led me to too, which is why I thought doing something I would never usually consider might actually be okay in this context

[TowerSales]

10 minutes ago, Ralf said:

The problem with that psu and adapters are that's it's 3 rail psu. 12VA=18A, 12VB=16A, 12VC=8A and max combined wattage is 385W, you would need to find out which rails go where so that you dont overload them.

And how would I go about doing that?