Update: AMD has sent us a statement regarding the PCIe power draw, saying: "As you know, we continuously tune our GPUs in order to maximize their performance within their given power envelopes and the speed of the memory interface, which in this case is an unprecedented 8Gbps for GDDR5. Recently, we identified select scenarios where the tuning of some RX 480 boards was not optimal. Fortunately, we can adjust the GPU's tuning via software in order to resolve this issue. We are already testing a driver that implements a fix, and we will provide an update to the community on our progress on Tuesday (July 5, 2016)."
It looks like AMD could be in some hot water over their new Radeon RX 480 video card, with the card reportedly consuming much more power over the PCIe port than it should.
Ryan Shrout over at PC Perspective has done a great job on measuring the power directly from the Radeon RX 480, and not the entire system power like I, and many other GPU reviewers, do. PC Perspective explains how it captures the power directly, where they are "intercepting the power being sent through the PCI Express bus as well as the ATX power connectors before they go to the video card and are directly measuring power draw with a 10 kHz DAQ (data acquisition) device. A huge thanks goes to Allyn for getting the setup up and running. We built a PCI Express bridge that is tapped to measure both 12v and 3.3v power and built some Corsair power cables that measure the 12v coming through those as well".
They compared the Radeon RX 480 against the Radeon R9 380, and GeForce GTX 970 which all consumed around 150W of power in Rise of the Tomb Raider. When overclocked, the Radeon RX 480 was using up to 200W of power in the same benchmark. Using the RX 480 and testing at 1080p in Rise of the Tomb Raider, PCPer were seeing 170W of power consumption on the RX 480 along - with around 80W over the PCIe port on the motherboard (represented by the white line in the above graph). The blue graph represents the 6-pin PCIe power connector, which is providing 85W.
Considering the PCI Express specifications for the motherboard connection are that it doesn't exceed 66W, the RX 480 is far beyond the limits of the PCIe specification itself. And while there's doom and gloom posts on Reddit, Twitter, Facebook and everywhere in between, this much power consumption from the motherboard isn't going to see motherboards in gamers' systems across the world exploding.
When overclocking the Polaris 10 GPU on the RX 480 by 3.5%, and the power target by 30%, the clock speed was all over the place as you can see in the graph above. When overclocked, the Radeon RX 480 was consuming close to 200W in some cases, which is a huge increase over the 150W TDP of the card - and the specifications allowed for the 75W from the PCIe port, and the 75W from the 6-pin PCIe power adapter itself.
With more testing under their belt, PCPer report that when the Radeon RX 480 is overclocked, the motherboard is providing over 95W of power over the 12V line, while 5W is being delivered over the +3.3V line. This means over 100W of power is being delivered over the PCIe connection, which is something that taps out at 75W. The 6-pin PCIe power connection is also providing 100W, too. PCPer goes into some incredible detail, if you want to get into the nitty gritty of it.
Where to from here? Well, from the start I've always thought that AMD should've used an 8-pin connector on the Radeon RX 480 - which would've allowed 150W from the PSU, and 75W from the PCIe port. AMD could've balanced this, as well as AIB partners and custom cards, to draw less than 75W from the PCIe connection, and use more from the 8-pin PCIe power - but no, we're stuck with the single 6-pin PCIe power and these power consumption issues.
Considering the GeForce GTX 1070 is a far superior card and consumes the same amount of power as the RX 480, we have to wonder what AMD was doing when it discovered these problems. The card was ultimately, and obviously released - but there's no way out of it on the reference cards. The AIB partner cards are coming very soon, so it'll be interesting to see what they're capable of.