The following command(s) only turns on or off the first outlet. It does not turn on/off the entire Power Strip.

kasa --type strip --host XXX.XXX.XXX.XXX on

kasa --type strip --host XXX.XXX.XXX.XXX off

Command-Line Docs.:
To command a single socket of a strip, you will need to specify it either by using --index or by using --name. If not specified, the commands will act on the parent device: turning the strip off will turn off all sockets.