But if the PCIE device itself receives a startup signal from motherboard, it checks for external power(probably using the 7th and 8th pins), finds none and refuses to do anything else, to the motherboard it may look like an empty slot, no? Just speculating, I have no idea what im talking about. In 40XX series i think it may refuse to POST if you don't connect at least 3 cables to 12VHPWR, but as for 20XX idk and idk how motherboard startup process really looks like in modern age.And this exactly should not happen, at least not in my experience with different mainboards (not just supermicro): I would have expected the post/boot process to fail becuase it can't determine if there is another gpu and what gpu to use...