16 awg? I doubt you will find that. The wire in the wall on a 15amp circuit is 14 awg and that is rated to carry 1800 watts. 20amp circuit uses 12 wire. 18 gauge is definitely enough to carry 150 or so watts.
It is about amps not watts:
Wall// 150W/
1.25A/120V //PSU// 150W/
11.25A/12V //GPU
edit: 100% PSU efficiency to make it simple.