[Alchete]

Any harm in using a 90w power supply? I assume the NUC will regulate the power it draws and not rely on what the brick can supply at max draw, correct?

If the voltages match, you can use a 900W power supply if you want. At a given voltage, the wattage is just an indication of the max current capability of the power supply. The power supply only delivers the current that is requested by the HW, not the max current.

It's more important to match the voltages to the HW requirements and just be somewhere above the maximum wattage required by the HW.