I upgraded to an XFX Mercury RX 9070 XT and have an 850W power supply with four PCIe sockets, but it came with only two PCIe cables. One cable has a single 8-pin connector, while the other has two 8-pin connectors on a pigtail. The graphics card needs three 8-pin plugs. Is it safe to connect both plugs from the pigtail cable plus the single plug from the other cable, or could that overload the cables or power supply?
3 Answers
Using two PSU-side cables for three GPU plugs is common, especially when one cable has a factory-installed pigtail. A separate cable for each connector would be preferable if the manufacturer offers one, but don't assume another modular cable is compatible just because it has the same brand name. Modular pinouts can differ between models and using the wrong cable can damage the GPU or PSU.
That setup is generally fine on a quality 850W power supply: connect the two pigtail plugs to two GPU sockets and the single connector to the third. The PCIe slot also supplies some power, and the card's total draw is within what the setup is typically designed to handle. Check the PSU manual first, since some models specify exactly how multi-connector GPUs should be wired.
The best answer depends on the exact power supply model. Look for its cabling diagram or GPU-power instructions in the manual. If the manual shows a pigtail being used for a three-connector graphics card, follow that arrangement; otherwise contact the PSU manufacturer before running the card at high load.
The order of the GPU sockets normally shouldn't matter. Just make sure every connector is fully seated and avoid adapters unless the PSU manufacturer specifically approves them.