I have a 3D printer that uses the Meanwell LRS-150-12 (150 Watt, 12V DC) power supply (Datasheet: http://www.mouser.com/ds/2/260/LRS-150-SPEC-806177.pdf) and I am installing a power socket and switch on the AC input side. The distance between the PSU and switch is only 8 inches but I wish to use the correct gauge of wire for both that connection and the actual power cord to the wall.

It looks like 18 gauge PSU style power cords are the most common while 14 gauge cords are very thick and harder to find. Would it be safe to use either 16 to 18 gauge wire in between the socket and switch along with an 18 gauge PSU cable?

I know that power in is roughly power out with some power in lost as heat but I would guess that the AC current is about 150W/120Vac = 1.2Amps (I am in the US) but I believe I need to know the power factor in order to calculate the real value. All of the circuits I have dealt with have been DC so the idea of RMS and AC power (and the power factor) are confusing to me.

 

I have a 3D printer that uses the Meanwell LRS-150-12 (150 Watt, 12V DC) power supply (Datasheet: http://www.mouser.com/ds/2/260/LRS-150-SPEC-806177.pdf) and I am installing a power socket and switch on the AC input side. The distance between the PSU and switch is only 8 inches but I wish to use the correct gauge of wire for both that connection and the actual power cord to the wall.

It looks like 18 gauge PSU style power cords are the most common while 14 gauge cords are very thick and harder to find. Would it be safe to use either 16 to 18 gauge wire in between the socket and switch along with an 18 gauge PSU cable?

I know that power in is roughly power out with some power in lost as heat but I would guess that the AC current is about 150W/120Vac = 1.2Amps (I am in the US) but I believe I need to know the power factor in order to calculate the real value. All of the circuits I have dealt with have been DC so the idea of RMS and AC power (and the power factor) are confusing to me.

You should be perfectly fine with the 18 AWG cable. A typical AC/DC power supply is around 80-90% efficient. Even if we assume some terribly efficiency, lets say 50%, you would still be fine with an 18 AWG cable. Not only is your current going to be low on the AC side (probably around 2 amps or less), its also a short run like you said. A standard 6 foot 18 AWG cable should work. As a rule of thumb I THINK (double check if you were ever close to these numbers) 18 AWG = 7 Amps, 16 AWG = 10 Amps, 14 AWG = 15 Amps, 12 AWG = 20 Amps. A lot of variables of course affect the true max rating (insulation materials, ambient temperature, air flow over cable, length of cable ect.), but its a good place to start.