To use an example: the RMBP comes with an 85W power supply but it's CPU has a TDP rating of 47W and GPU a rating of 45W for a total of 92W. Without even gettin

To use an example: the RMBP comes with an 85W power supply but it's CPU has a TDP rating of 47W and GPU a rating of 45W for a total of 92W. Without even getting to powering other circuitry, the display, or including conversion efficiency, it's pretty obvious that it can't run full bore off the wall supply alone.