Motherboard power usage.

Solution
You can go by the chipset's TDP if you want (EDIT: actual mobo power draw is between ~10-50w), but motherboard power consumption is negligable really. If you're close enough to your PSU's limits that mobo power draw starts to matter you'll want to upgrade anyway.

EDIT2: Dug up an old thread with this quote in it, since you wanted research ;) :

Vexillarius

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You can go by the chipset's TDP if you want (EDIT: actual mobo power draw is between ~10-50w), but motherboard power consumption is negligable really. If you're close enough to your PSU's limits that mobo power draw starts to matter you'll want to upgrade anyway.

EDIT2: Dug up an old thread with this quote in it, since you wanted research ;) :
 
Solution