Hello, thanks for choosing Dell. As far as I know we have two cables for R740 GPU.   TR5TP ASSY,CBL,PWR,DW GPU1,RSR1,R740   VM577 HRNS,WRNG,CON,PWR,GFX,FF2.0,NV / Auxiliary Power Cable, Luxshare Precision Industry Co, (NVIDIA FF2.0 to PCI-E STD Power)   However, I'm afraid there's no way of telling which is what you want since you are trying to use a non Dell part.
Dear Team  I want to connect ALVEO card With DELL EMC R740. i need one PCIe AUX Power cable to interface .  kindly suggest some cable part number. in the screenshot please check cable layout. [IMAGE][IMAGE]     
DELL EMC R740 supported PCIe AUX Power Connecter