How is GPU power draw distributed?

[Blaze200038]

So I have a general question that I'm curious about, and a particular problem I am trying to solve with that question.  The question is, if I were to plug a card with a PCI-E 6-Pin connector in to my board and PSU, will it draw more power over the board connection, the PSU connection, or evenly between the two?

 

The particular problem I am trying to solve is whether I can add a cheap power supply to an underpowered system, thus allowing me to use a more powerful graphics card.  To be clear, this secondary PSU would not be supplying power directly to any of the motherboard connections- only the PCI-E 6-Pin, fans, and SATA power.

 

Any information on the first question alone is greatly appreciated, though if anyone has advice for my bigger problem, that'd be rad.

 

Full janky system details if you want to dive deep:

Spoiler

MOBO: Supermicro X7DWU

CPU: 2x Xeon E5450's

RAM: 8x4 Gb DDR2 FB-DIMM's

GPU: GTS 450

PSU: 430 Watt EVGA + 300 Watt Delta

HDD: WD 500 Gb IDE + Hitachi 160 Gb SATA II

COOLING: 6x 120mm fans, 2x SNK-P0025P 2U Coolers

 

Now, if you've read this far, you might be wondering why I'm even concerned about increasing the graphical performance of my 10 year old server.

And I have no good response.  Any advice?

 

[tikker]

Don't. Althought EVGA and Delta (iirc) both make good PSUs, just get a single more powerful one. It saves you a lot of trouble.

[cj09beira]

you could and i have done it in the past, but both psus seem too small, it the one you are trying to add natively has the 6 pin you could do it but if it doesnt dont do it, the power distribution depends on the card, but most cards power the core through the 6 pin and memory and other small voltages using the pci slot

[Jonathan Lemmens]

1 hour ago, Blaze200038 said:

So I have a general question that I'm curious about, and a particular problem I am trying to solve with that question.  The question is, if I were to plug a card with a PCI-E 6-Pin connector in to my board and PSU, will it draw more power over the board connection, the PSU connection, or evenly between the two?

On most graphics cards there are separated circuits, meaning the core power will only be supplied trough the 6pin, memory and aux power will generally come trough the mobo. In this case there is no way for the card to pull more power from the mobo to compensate for insufficient 6pin-power. 

1 hour ago, Blaze200038 said:

The particular problem I am trying to solve is whether I can add a cheap power supply to an underpowered system, thus allowing me to use a more powerful graphics card.  To be clear, this secondary PSU would not be supplying power directly to any of the motherboard connections- only the PCI-E 6-Pin, fans, and SATA power.

You could, and I did it once, but I would never use this as a permanent solution. Also, both PSU's are a bit on the weaker side, I would advise to get a single more powerful PSU for the whole system.

[Blaze200038]

9 hours ago, Jonathan Lemmens said:

On most graphics cards there are separated circuits, meaning the core power will only be supplied trough the 6pin, memory and aux power will generally come trough the mobo. In this case there is no way for the card to pull more power from the mobo to compensate for insufficient 6pin-power. 

Wow, that is super useful to know.  Thanks!

9 hours ago, Jonathan Lemmens said:

You could, and I did it once, but I would never use this as a permanent solution. Also, both PSU's are a bit on the weaker side, I would advise to get a single more powerful PSU for the whole system.

10 hours ago, tikker said:

Don't. Althought EVGA and Delta (iirc) both make good PSUs, just get a single more powerful one. It saves you a lot of trouble.

I whole-heartedly agree, this is not an ideal solution.  The main reason I am considering it is because I already own both PSU's and I don't want to spend any more money on what is essentially a closet-warming hobby build that I'm still not sure what I'm going to do with when it's fully operational.