I discussed exactly that spec already in your quote of my previous post
. And as you can read on top of the table, that are
requirements, the slot has to be able to fullfill. In principle, nobody forbids some system designer to include higher quality slots than required by the spec. That would allow the card to use more if that is somehow communicated to the card. Before a higher power draw is negotiated, the card has to limit itself to the requirements set forth in your table. Something like this is actually described in the PCIe base spec (I posted a screenshot of a section with it). A card is allowed to use whatever is higher, the slot power limit set by the BIOS or what the form factor spec (i.e. the PCI Express Card electromechanical spec) allows.
From my quick glance over the ~900 page document of the base spec, it appears to be slightly inconsistent and I agree one can read it as if the "slot power limit value" in the slot capabilities register the BIOS can set for each individual PCIe slot in the system may include not only the power supply through the slot but also the supply through additional power plugs (even when I would deem this a somewhat strange way to specify a "slot power limit" for a mainboard). But frankly I can't be bothered to look in detail at the in total more than 1000 pages that makes the PCIe spec to figure that one out for sure, especially as it probably doesn't bear to many practical consequences.
The practically important question is, what are the actual current limits of the PCIe slots on normal mainboards. I have said already, there are some slots on the market, which barely fullfill the PCIe electromechanical spec. That would mean, with such a slot it can get problematic to draw +50% of the rated current (in case of OC) over the tiny contacts in them, especially if they are worn out a bit already, for instance by repeatedly exchanging the graphics card.
There is a difference between PCI express spec and ATX12V V2.x spec and also the Molex connectors, the latter two specs are not applicable to the PCI express slots.
Therefore it is not unexpected that the PCI express slot is close to the sustained 5.5A current specification as it is integral to PCI Sig for 66W through the 12V, and different to the ATXV12 spec and standards that can be substantially higher IF following the component standards I mentioned earlier.
If looking at 150W and higher, these fall into the 150 W-ATX Specification/250W to 450W configurations part of the ATX12V publications, it is not just the PCI express you look at.
And in these publications it also specifies HCS that you will not find on lower mainstream boards and PSU.
Again there are two primary considerations;
1. The PCI Express slot that has tighter values in terms of manufacturers implementations giving 66W over the 12V and 9W from 3.3V - yeah 85W sustained and shown by Tom's Hardware and some extent at PCPer is eye raising and compounded as it should be acceptable to some systems but not all, also would not want it to be any higher though as it is already pushing it to the extremes.
2. The ATX12V 24-pin connector mostly in context of 2x480, but also potentially when looked at from the budget motherboard and PSU focus with a single 480.
2. a) This is shared with all PCI express slots and other devices that do not have their own separate power.
OCing or adjusting the power target (even without OC) would be applicable to both situations and not necessarily just budget boards.
Only the ATXV12/Molex connectors could be deemed to have a rating closer to 8A per 12V contact for the PEG connectors (total 192W for 6-pin and 288W for 8-pin), and a bit less at 6A for the ATX 24-pin 12V contacts (gives total 144W) if it is not HCS (that was specified under ATXV12 v2.2) - There is also a higher threshold for moderate sustained duration bursts beyond max current for the ATX 24-pin and PEGs.
Just to raise a separate point,custom AIB will not overcome this problem by implementing an auxiliary PEG 8-pin/2x6-pin/etc configuration unless they also re-define the power distribution and ease preassure off the PCI Express slot, this is going to be critical with AIB partners as it is more than likely they will at a minimum increase the power targets and possibly some small OC.
CHeers
Edit:
And to re-iterate, if the 480 is left in standard form it will be fine for most including many mainstream consumers (IMO just needs a careful look at when matched to the lower end of mainstream motherboards and PSU).
That means not increasing power target and not increasing clocks, and using 2x480 only with very good motherboard and PSU.
