I'm actively considering this solution. However, two problems exist:You need to take into account the 75W each PCIe MB connector provides for GPUs with no added power cable.
2x75W PCIe 16x slots, plus 2x 75W, 6 pin PCIe cables =300W total for 2 GPUs. Or 1x75W slot and 150W cable (2x6, or 1x8 pin)=225W single GPU. That's what the dell specification means. The T7610 doubles that.
So the MB cable provides 150W (2x75W 6 pin )officially. I'm not seeing 300W on that cable officially from Dell.
6+8 pin would be a 75W stretch. 8+8 pin would be double the rated power. The 300W 6+2(8) and 6+2(8) cable IS available, it's FOR Dell, but not FROM Dell. For the OP who just needs a few Watts over the rated 225W it's a good solution. But if you tried to run 2x225W 8 pin GPUs there's no guarantee it would work.
Here's something I found that may be useful. The computers using those 685W power supplies have a PSU card in between the PSU and the MB. The T5610 card has a 2nd CPU 8 pin connector.
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The extra CPU connector could be adapted to power a bigger GPU.
The T3610 card doesn't have that extra connector. It should also allow the T5610 optional 825W PSU. But w/o the 2nd CPU probably not needed. Warning- The CPU 8 pin pinout is not at all like the PCIe 8 pin. Don't plug the same cable into it.
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1. Are the plug definitions for the T3610 and T5610 the same for the 24-pin motherboard? I'm considering swapping the power distribution board for my T3610. (Based on my understanding to those russians listing them together when testing mb voltages I think they are the same)
2. Are you sure Dell uses standard EPS here? If so then I can surely find an adapter to convert EPS to PCIe 8pin to feed the GPU.