Hi @kaczorefx,

See if I could help answering your question.

1) Why would the PCI slot care how many aux cables the card needs?

The PCIe slot actually cares about how many current passing through as too much current may break the system. W(power) = A(current) x V(voltage). While voltage fixed at 12V for x16 slot, current would be the valuable for watt values. Therefore, "300w" means how many power accepted but not provided. Further reference on Wiki:

2) Also why does the second slot support only 225W?

I understand your feelings being confused.

Online support reference tells slot2 at 300w and slot4 at 225w

Technical Guide tells "It has two native Gen 2 PCIe x16 graphics slots each capable of driving graphics cards up to 225w".

Even worst, Spec sheet and Service Manual tells nothing about it...

Not sure why there's a difference here. But I guess, just a guess, it's the difference between max power support on a single slot and the whole system. Take my T5600 as example, there's a wordings in the T5600 Techincal Guidebook stating that "Total allowed graphics power allowed in slot 2 is 225W. Total graphics power allowed in system is 300W." Maybe it's the same case on T7500. Just maybe ^^"

3) What about the x8 slots? I hope they supply also 75W.

Yes, I understand again that all documents above say nothing about x8 slot. I also checked on the mainboard screenshot and same result:

However, this thread explained "All sizes of ×4 and ×8 PCI Express cards are allowed a maximum power consumption of 25 W." Therefore, sorry about it ^^"

4) Anyone mounted a GTX 1080 or 1080Ti in one of the x8 slots?

Take my T5600 experience as reference again. When I 1st install a RTX 2070 into slot4 of my system, it runs into Windows with no problem. But when I run GPU peak benchmark test, the system broke down and reboot immediately. Then, when I swap it to slot2, everything's fine again. Later I realize that slot4 of T5600 is actually "x16 (wired as x4)". Too much current detected by the PSU distribution board during GPU peak test and thus stop all power supply. Good job for the distribution board or my house would be burned!

Therefore, as mentioned above that x4 and x8 slots take the same limitation on power consumption, I'm afraid GTX 1080 or 1080Ti won't work on x8 slot. Better don't try.

Sh^%$^%ugar.

So that would mean I also can't install 1080ti or 2080ti in x16 slot4, which would be nice since a double slot card in it would overhang A PCI-x slot which is useless anyway.

But I can't do that because the cards are 250W - I have to mount them in slot2, which will cost me one of the x8 slots - who designs these boards?? It's a workstation and you can't even install two top cards in it!!!

Although the 2080ti has 2x8pin aux sockets, so at least it can get all of its power from them.

Your configuration probably bombed because 2070 is 175W and has only one 8pin, so this and your x4 25W PCI was exactly 175W - the test might have drawn a little more, so you were actually lacking on power, that's why PSU shut it down.

So now a new question, has anyone tried installing a 1080ti or 2080ti in slot4 in T7500?

Why is slot 2 blue and slot 4 black? 

Dose 2 have a lower IRQ/FIQ? Did they run out of $COLOR plastic?

Interesting guess about short of plastic :BigSmile:

The blue color of a PCIe x16 slot stand for the default slot for GPU, and it used to be a common standard of motherboard. That means slot 2 default for GPU and slot 4 optional.

Due to card size and limited rooms within my T5600, I do have to install GPU on the optional slot.

And it work in that configuration 

T5600