“Pocket socket” just means any device that plugs into an existing wall socket and that you then can plug a non-networked device into to give you networked control.
I like the term “pocket socket” because it makes it really clear when we’re talking about one of the plug-ins and not a receptacle that is wired into the wall. But different manufactures call them different things, from “modules” to “plug-ins” to “smart switches” to “pluggable outlets,” all of which can easily be confused for other things.
The following thread discusses the typical features of this device class, with a number of pictures:
They typically cost anywhere from $20-$60. The ones that are Z wave plus will have the longest range.
www.zwaveproducts.com has a good selection in their lighting category, but pretty much any place that sells zwave devices will have some, including Amazon. Prices vary a lot on the same models, so shop around.
Remember that Z wave repeats only for Z wave, zigbee repeats only for zigbee, and Wi-Fi pocket sockets like wemo will not repeat for anything. But all zwave versions are backwards compatible, so a zwave plus pocket socket will repeat for older generations of zwave as well.
The community created wiki has an article on repeaters that lists some specific models
