I have a cheap PSU of this sort, used for my 3d printer. It has a 110V input, and a 12V output with 20A maximum current. Unfortunately, it doesn't have detailed specs/data available beyond that.
Now, I would like to place a simple ON-OFF switch (like this) at a convenient physical position, and in series with the AC power line.
Of course, it's important that the switch I choose (for example a 3A-rated one) is safe enough for the input current of the PSU. By conservation of energy, can I assume that the input doesn't draw more than (12 * 20 / 110) = 2 to 3 A? Or will it be significantly more than that, since I'm underestimating losses in the form of heat?