not sure if you mean a desktop or a laptop but the following applies either way
if you do a full shutdown of your system you can unplug the power cord from the wall, should not affect a quality power supply (desktop) plugging it back into the wall afterwards, if you mean you do this a lot, I would suggest turning the power supply switch off, because repeated plug unplugging can possible cause a "jolt" of incoming power and a low tier psu could get zapped and you would have to replace it.