Power supply could be any size you want, it's the parts that draw as much power as they need. MB may not be able to handle enough power for CPU or PCIe slot (75W).
That's like saying that light bulb would burn because gets power from hydro electric plant that makes mega and gigawatts but that is obviously not happening.
If you need more power because of a GPU that requires separate power input, it's not overloading MB but draws power directly from PSU.