The PCIe graphic card standard (which has nothing to do w/ ASICs) limits power to 75W on 6 pin connector and 150W on 8 pin connector (using no more power pins) however those are artificial limitations.   The actual connector is good for 9A per pin, 3 power pins (both of 6 & 8 pin connector), 12 V means 324W (9*3*12) per connector max or 648W for a pair.  

Now how much power a particular PSU can push to the connector is another question.  The VRMs on the board also have a max current limit so the chip can only be provided so much power but the connector is a total non-issue.