I really don't need electronics lessons. I have actually measured the power draw of a number of cards. You said the powered risers power the motherboard, that is false. Most powered risers, including the USB ones I sell, do not even have any power connection to the motherboard, they only even connect to the gpu. The data signals are passed along the USB cable.
Ahh I see. Your risers have their own powered slot. The ones I'm used to seeing simply have the 12v line soldered directly into one of the 12v pcie pins on the ribbon cable.