Bamming1 :
bliq :
Yes, 802.11ac USB adapters are backwards compatible with 802.11b/g/n (as long as you don't configure it to "ac only" or something like that)
you mean outlet adapters?
No, the unit itself is called a "Network Adapter". The one you are talking about plugs into the USB port so they're technically called USB Network Adapters, or USB adapter for short.
As for are they making USB 3.0 ones, the answer is yes because the newer N and AC standards allow for speeds that exceed USB 2.0's max of 480mb/s. The fastest N and AC can do 600mb/s on 2.4 and as much as 1300mb/s on 5 (at least theoretically, practically its much less).