No special considerations with the Mean-Well type 12V supplies. They'll turn on when AC is applied to the input terminals. You don't have the complexity of the PC-type power supplies where you have to short pins together to act as a power switch or put a load on the 5v supply in order for the 12v output to be in spec.

I also have a power switch in line with the AC wiring. You can see it in some of my build pictures on the upper part of the front face - sort of where the MakerFarm spool holder goes. Is there any kind of label on the power supply saying what it can draw as far as AC current? If so, going with a switch rated for at least that at 120VAC would be the safest way to go. FWIW, the datasheet for my 320-watt MeanWell says it can draw up to 6 amps. Whether you use push-button or toggle is based on personal preference and on what you can find if you're looking locally like at Ace Hardware or Radio Shack. I'd be wary of an auto store - many of those switches may only be rated for 12VDC and could arc if used at 120V.