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This cable 1 works fine to power a PCIE accelerator device (Intel N3000-N FGPA PAC) on Dell PowerEdge R720. The power connector that plugs into the riser seems to break power cable/port standards/conventions. This led to a lot of trouble for us when we decided to plug in the FPGA in a different server. I wanted to confirm if indeed Dell breaks the convention/standard.

Figure of the end that plugs in to the Dell server riser: Dell power cable

From this figure, we can see that pins 1,4,6,7 on the board must be square holes. We can also see that the yellow wires (assuming +12V, see below why this assumption is correct) are away from the notch (i.e. pins 1,2,3 are +12V).

The keying 1,4,6,7 square holes matches a CPU power port (the pinout does not). While the pinout 1,2,3 12V matches a PCIE power port. For reference the keying and pinout of standard CPU (EPS12V) and PCIE power ports are here: enter image description here

The cable is advertised as 8 pin CPU to 6/8 pin PCIE power cable. The 6/8pin PCIE end conforms to the standard. The CPU end which plugs into the motherboard has the keying/shape of the CPU port but the reverse wiring/pinout (i.e., wiring is as if it was a PCIE power port).

If indeed Dell mixed the standard. WHY WOULD THEY DO THIS? WHAT MOTIVATION DID THEY HAVE?

Why yellow wires must be 12V: This is the figure for the other end (6/8 pin PCIE) of the same cable: enter image description here

We can see that wires away from the notch (pins 1,2,3) are yellow. The FPGA documentation (page 8 of 5) clearly mentions pins 1,2,3 are 12V. Since the NIC works fine with this cable, it would mean that its getting the right power supply and so the yellow wires (1,2,3) must be 12V.

Edited: For more clarity, please refer to the image here: PCIE, EPS12V, and Dell MB power ports NOTE this image shows ports (female) not cables (male). The pin numbering is mirror image of the reference above which shows cables instead of ports.

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    \$\begingroup\$ Have you measured continuity to check that the pinout is as you expect? Otherwise, I expect it's probably more of Dell being intentionally incompatible with existing standards, as I've heard they often do... \$\endgroup\$
    – Hearth
    Oct 15, 2021 at 18:30
  • \$\begingroup\$ Likewise, this cable: store.supermicro.com/… is advertised as 8pin CPU to 8/6 pin GPU/PCIE. However, both the ends resemble the shape of PCIE port (1,7,8 square holes). Why such discrepancy? \$\endgroup\$ Oct 15, 2021 at 20:49
  • \$\begingroup\$ Hearth. I only see cable colors at both end points. I assume cables don't change colors in between. Based on this the pin layout is as described in my post. If dell intentionally violates standards, I think there should be a body that regulates/enforces these standards and penalizes violations. This may be too extreme though, I don't think for any standard there is penalty on violation, you just won't get customers for non-standard products. IDK whats the best solution around this. \$\endgroup\$ Oct 15, 2021 at 23:20
  • \$\begingroup\$ I would still double check with a multimeter set to continuity mode. But Dell has been violating standards on purpose for a while; as I recall they don't even use standard SATA connectors for hard drives in their prebuilt desktop PCs. \$\endgroup\$
    – Hearth
    Oct 16, 2021 at 2:24

1 Answer 1

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EPS-12V is a non-ATX server standard. It is used as a generic, high-performance 12V connection in servers and sees adoption in desktop supplies as well.

More here: https://forums.tomshardware.com/threads/what-is-eps12v.217277/

That said, it's simple enough to use an adapter cable to connect EPS-12V to 6- or 8-pin PCIe/GPU power. The sense lines are only used on the GPU side, and the pinning prevents plugging in the cable incorrectly.

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  • \$\begingroup\$ This does not answer my question. The dell cable has shape of EPS12V port, but the pinlayout (12V/GND) of the PCIE port. This seems to break the convention and I wanted to confirm if indeed dell breaks this convention. I understand that cables convert between different port types. My question is separate from EPS12V vs ATX. I want to understand what is the definition of the EPS12V port, the cable and standard image seem to disagree. \$\endgroup\$ Oct 15, 2021 at 20:52
  • \$\begingroup\$ The cable you're referring to is EPS-12V on one side and PCIe GPU on the other. There is no issue that I can see, the cable seems to solve your problem perfectly when the power supply is using EPS-12V standard. My desktop power supply also uses EPS-12V, and I use that same type of cable to power GPUs. \$\endgroup\$ Oct 15, 2021 at 21:19
  • \$\begingroup\$ I agree on one side it is PCIe GPU, IMO, the cable is NOT EPS12V on the other end. This end has same shape as EPS12V. But if you see the wiring closely, you will observe that yellow wires (+12V) are at the bottom (away from the center clicking notch, pins 1,2,3). Where as for EPS12V, the +12V pins are on the top (near the notch, pins 5,6,7,8). \$\endgroup\$ Oct 15, 2021 at 22:10
  • \$\begingroup\$ These are EPS12V (CPU) to PCIe GPU power cables: store.supermicro.com/…, store.supermicro.com/…. Notice that on the EPS12V (CPU) side (blue/white color connector) the green/yellow wires are near the notch (pins 5,6,7,8), i.e. opposite pin layout as the Dell cable, but same shape (pins 1,4,6,7 square hole). \$\endgroup\$ Oct 15, 2021 at 22:15
  • \$\begingroup\$ hacktastical please let me know if after my explanation you still think there is no discrepancy. \$\endgroup\$ Oct 15, 2021 at 23:02

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