PCI-e power = 75w
6 pin = 75w
The Rx 480 uses the power from the PCIe and 6 pin. Hence it should be 75w+75w = 150w
However it is drawing around 90w from the PCIe when stressed. Even reaches 100w if overclocked. More than the maximum threshold.
That leads to 90w+75w = 165w
The consumption of 90w on something designed to only supply 75w is concerning.
The Motherboard can get severely damaged. Not only the motherboard but things like the CPU and RAM may also get damaged.
If thats not bad I dont know what is.