I measured that some years ago. It was ~60W or so pulled through the slot for a card with two extra cables running to it. Specifically I measured the current do

I measured that some years ago. It was ~60W or so pulled through the slot for a card with two extra cables running to it. Specifically I measured the current down the wires and subtraction gave me that as a reasonable estimate for the slot. Won't be perfect but pretty sure it's non-zero through the slot.