did you really post this 4 times, if yes why?  stick to one post please or update 1 post with added comments to bump it up.

first never just throw in, a GPU cards. ok>  (I guess you want only 1 card to work, )

first off the cards must never exceed 75watts in the PCI-e (this is classic this limit on any PC made or server)

if the card has AUX power connector as this one does, that needs power, from the PSU, that has no such connector. (this server i bet has no proper GPU 4/6 or 8 pin AUX power connector.  (some 8 pins use -5v and -3.3 volt took, so do not guess or you will blow things up) see that in wiki aTX PSU spec.

this rack server is no gaming PC.

the 690 uses 30amps or current on that jack, if not connected the 690 will be dead. lack of power.

you can never suck 30 amps off any PCI slot, ok>?  only about 6 amps (typ)

you forget that the 1000watts never lands on the PCI slot with that power level ever.

no riser P/n stated, some riser slots are not PCI-e at all but Dell proprietary for RAID cards only by dell.

I take it you threw 1 at a time many GPU cards at the server,

your results are fully expected,

It may be possible to hack in and external PSU with the full 30amps feed on the AUX connector

with the case grounded to the server properly and all but I wouldn't .

I'm pretty sure it just posted once. I updated the tags and that may have made it look like it posted more than once.

My PSU actually did come with two 8 pin connectors connected to the 12V bus, and two 6 pin connectors as well. I'm not using the server to game, but do ML model training. The GPUs I used for testing were to see if the PCI slots were functional before I bought a proper training GPU. 

I've also diagnosed the problem of the second riser being completely non-functional. I believe that installing a processor into the second (currently empty) socket should enable the PCI slots. I have one on order (yes its the exact same part as the processor in the first slot). They won't be a matched pair, but I'll see how it works.

I've gotten an Nvidia Tesla C2050/2070 running. It required a 6 pin and 8 pin connector, but booted up just fine. I believe the issue with the 690 may have to do with the fact that its a Dual GPU card with some more intense power requirements. 

Do you have both power supplies plugged in? put the gfx card in slot4 and it should work. I have a 1080 working in my single 2697v2  r7610.

You need the second cpu to use the second pcie riser

wish i get some help here

i have the excact same PC, with 2 Processors , however Centre riser not detected

went through the bios, but no setting for such

wish someone can help

cheers

have a nice day