VESA's "standards" indicate power is to not be supplied/returned over Pin 20. The GPU would be supplied power from the display and the motherboard, often - but not always - at differing Wattages and Voltages. DP "standards" are a subset of VESA's "standards".
I contacted VESA, which related that some of the cables we were using were likely not compliant, and sent me this text:
"Power is provided by the DisplayPort connector on both the Source and Sink side (500mA at 3.3V, which is 1.5 watts). Power is not carried through a standard DP cable, otherwise the Source and Sink power supplies would conflict. Power is carried in a MyDP cable, however, to provide power to the MyDP Source (such as smartphone or tablet). Power is also used by a DisplayPort display adaptor by the Source, or for an active cable. Power is also used for a DP-to-optical converter at the Source, and optical-to-DP converter at the Sink and can be used this way for other signal conversion as well at either end. Power is not, however, carried through a standard DP cable. For one, there is no need for this and two, problems can result as described above."
I often write construction contracts, and can often identify "boilerplate" or "uniform" language as I'd seen in that message from VESA (and it was sent in minutes, and nobody types that fast!), and found this lengthy post over at rage3d's forums, courtesy of Google:
http://www.rage3d.com/articles/amd_eyefinity_displayport_difficulties/
which led me to bust out my own multimeter and start checking for myself. We had issues with our AMD cards every day (our CAD production machines use Quadro cards), and quite often with our nVidia cards (on both Macs and PCs) - the poster has some experiences quite similar to those I had. The post was made over 3 years ago, is a good read, and makes me wish I'd seen it sooner. There's other similar posts at Anandtech's forums and (H)ardforums.
Beyond that, most - but not all - of our displays put out power over Pin 20 (including my Dell displays) which means
to me that they are also not VESA-compliant, a point that I haven't even tried to make in these forums. The Eizo displays and the cables that shipped with them do not return power over Pin 20 - no power whatsoever, and the BenQ BL271U displays also do not return power over Pin 20 (we just used the Accell cables already connected to the PCs with these BenQs). After a bit of my own investigation in my company's logs, the PCs connected to the Eizo displays never (or very rarely) BSODed or needed a component replacement outside our normal routine maintenance - and I can report that we have had sleep/overheating/freezing issues with the Dells. I'm not buying any more Dell displays because of this last point, at least not for the foreseeable future.
Now I'm thinking I'm going to start up a distillery - my chemistry is much better than my electrical skills...
