AMD's RX 480 fails PCI-E specification
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And what does it really mean, what happens if the cards takes more power? - Will the power rails on the board/psu regulate it down?
It all smells a bit.
It doesn't mean much other than potential recall/legal issues for AMD.
And no motherboards will not restrict it, it can cause motherboards to become unstable since many more things share the PCIe power bus other than the GPU (high end motherboards usually have extra power connectors for multiple card setups) and it can damage the motherboard physically if the traces are not rated for that current.
The problem here is you combine a low end card with borderline spec issues, this means that virtually everyone who'll own one will own a low to mid range motherboard also which are the ones which are likely to have issues.
High End motherboards are so overbuilt for overclocking and multi GPU setups that it doesn't really matter, but with 10-20% more draw on the PCIe power tracers even the reviewers were nervous testing the cards on those rigs.
We need to see if the non-reference design cards also suffer from this problem, but it looks like the commercial release reference design cards suffer from this issue also.
To compete with the 1080 AMD needs to release a 300-350W card, and from the looks of it to compete the big die 1080ti / Titan P that would come out they are looking at 400-550W cards.
Keep in mind that the 480 is already their "small" die on a 14nm FinFET process there is nothing more to shrink at this point.
The R480 is still a great card 200$ for GTX970 superclocked performance isn't bad atm.
I'm thinking this is going to be a repeat of the R79XX series, where AMD can't compete with NVIDIA on single die cards and they'll release a dual die card. My own theory is that AMD will rebrand the Fury X2 and release it to compete with the 1080/1080ti's since Polaris looks to be way too power hungry atm.
This issue caused a low end machine that a reviewer built to shut down: https://www.youtube.com/watch?v=rhjC_8ai7QA
Reported to cause damage to older motherboards: https://community.amd.com/thread/202410
AMD has published a short message saying that they are looking in ways to "fix" this via the driver. The drivers have a profile for clock and voltages at any given setting so it looks like these cards are going to be "downclocked" or the voltages going to the memory and GPU adjusted down for given clocks in order to prevent the card from peaking above 150W.
This doesn't look good for AMD to be fair they should recall these cards and redesign the boards. GPU cards tend to stay away from topping the power consumed from the PCIE bus for good reasons they don't want to bet on the stability of motherboards especially with everything and their mother being interconnected via PCIE these days.
NVIDIA cards usually top at ~30W or so, single power connector AMD cards from the previous gen used to top at 50-60W.
I really don't understand how this passed internal testing or even the design phase, pretty much every engineer would prefer sucking more power directly from the PSU than from the much thinner tracers on the motherboard...
EDIT: Apparently the motherboard tracers aren't the big problem especially on high end motherboards which have a very thick power plane.
The power spike can however damage the PCIE slot itself mainly the pin's as the electromechanical spec for the PCIE sig dictates the exact specification for the pins on the slots even higher end motherboards might be damaged (slot damage like the ones reported over on the AMD forums) if there is too much current draw as the pins are likely to overheat and can either melt down or melt the plastic around them and cause the mechanical connection to fail.
Higher end motherboards however do have a better power phase so they are less likely to shutdown with these cards.
My personal recommendation is if you have purchased the reference design of this card use the 30 day money back policy and send it back. The driver update from AMD might fix it but it also means that your card would likely suffer performance wise at least in some circumstances. Wait for a new reference design or for non-reference cards to come out if you are still interested in the RX 480. You'll get a higher performing card or if AMD decides to gimp all RX 480's via the drivers you could at least safely overclock your non-reference card to the original clocks and higher.