Outlet to Outlet/Switch Combo
Existing outlet should have black (hot), neutral (white) and ground. All grounds always go together and are never switched, so we can ignore them for this answer (but do connect them all together).

Change the hot &amp; neutral going into the outlet to pigtails. Each single wire goes into a wire nut along with a short wire (same color) going to the outlet as well as a wire (same color) going to the new switch box.

The new switch box will have two sets of wires coming in:


Black/white pigtailed as noted above to the old outlet.
Black/white going to the new, switched, outlet. Black normally goes to the brass screw, white normally goes to the silver screw. Don't use the backstab connectors as they are less reliable than screw terminals.


Wire nut the two whites together. You don't need them now, but you will in the future if you ever put in a smart switch.

The black from the old outlet goes to the switch ("line" if you have "line" &amp; "load"). This is the hot.

The black going to the new, switched, outlet goes to the switch ("load" if you have "line" and "load"). This is the switched-hot and you may want to mark it differently (e.g., red or some other color besides black, white or green) on both ends so that anyone looking at it later will know that it is a switched-hot and not a regular hot.