There are other types of 12v power supplies. the MeanWell mentioned is common and simple to use.
you connect 120 VAC to the AC input and 12VDC to the output
There is one point about 120 VAC. trying to eliminate myths and opinions. the NEC or National Electric Code requires that 120 VAC be isolated from any voltages under 54 volts. this is very simple to do, you may have seen cardboard inside of a TV set that separates the two voltages.
In the hobby world, we are concerned that a stray wire or slip of the screwdriver might make your work, exciting.
It is good practice to limit low voltage wires in the AC side of the project to only wires that need to be there. and vice versa.