Zyxzenze,  An issue you may run into is that the specific GPU isn't supported, and may not function. The supported GPU list for the R730 is below; Nvidia GRID K2 Now so you know, the R730 can support two 300W, full-length, double-wide or four 150W, single width GPUs. The GPUs are installed on the PCIe x16 Gen3 interfaces available on Riser2 and the GPU-Optional Riser3. For installing two internal GPUs in the system, GPU-Optional Riser3 has to be present. It also looks like the cables will be GPU specific as well.  Let me know if this helps. 
Dear Sir or Madam,I have bought the Poweredge R730 w/ Single E5-2640 V4 (10C/20T) with 750W 80+ Platinum PSU config and perform well. Now I wish to add the GPU card for extended processing performance, eg. GTX1080 with typical 170W. I have searched the Dell community and external forums and found there should/might be an external power problem based on custom GPU installation. Those I need to inquire you on: should I have to order the GPU Installation Kit or any part to ensure the custom configuration gets into work (optional 2x GPU should be concerned). I acknowledged that the GPU installed might be used only for processing task and not for display purpose.Thank you for your kind forward assistance.Sincerely,Worapong Wilairat
GPU Installation on R730