Does this come with 2 units?

Technically there are two units - but one gets plugged into the router. If you actually wanted to be right next to the router, you'd plug your device into the router and/or have such good wifi as to not need this at all. So in practical usage there is one unit that you can legitimately use for the purpose of having a remote wired connection away form the router. These are expandable, by buying additional units. So buying 1 set gets you router mounted + 1 remote, buying two sets gets you router mounted + 3 remotes, etc. Just always keep in mind that you lose 1 unit to the need for it to be connected directly to the router.

Can someone tell me what this does?

Depends on which version you refer to. The PLW1010 has WiFi capability, the PL1010 does not. They both have an ethernet port. The base unit is located near your router - use ethernet to connect the base unit to your router to get the best throughput from your router and into the house wiring. Plug it into an Electrical outlet and it sends your LAN signal through your house wiring to be picked up by the remote unit(s) plugged into wiring elsewhere in the house. The remote unit has an Ethernet port, so you can attach a Smart TV, BluRay, Game Console, whatever, to the ethernet and get pretty good network response (probably not gigabit, but pretty good anyway). With the Wifi Version (the PLW1010) the remote unit ALSO transmits WiFi signal. I have not purchased this WiFi product yet, I have a ethernet only version right now and looking at this to expand my iPhone/tablet Wifi signal in remote parts of the house). As such, I have an older house and the electrical wiring is sketchy and is rather noisy and fluctuates, but this technology seems to work nonetheless even on the other side of the house, I even have had the base unit plugged into an extension cord and it still works. So bottom line, this will extend your LAN signal to another room of the house via ethernet, and the WiFi version also creates a WiFi Access Point in that remote room. From what others say here, that Wifi is an extension of your router WiFi in SSID/pw. I hope this answers your question.

If I buy two of these kits will I have 1 sender and three receivers or 2 pairs?

Keep in mind, the video on a product page misleads customers! You can't buy WiFi PL extender PLW1010 as they say in Video. If you buy two kits, you'll have - one powerline LAN distributor (non-wifi) - two WiFi extenders (each: PL receiver + Wifi broadcasting + 1 Ethernet Port) - one powerline receiver (non-wifi) you can plug to the power outlet and use as single Ethernet port

Will the top of the Powerline 1200 block the ground terminal of the upper outlet of a wall socket if plugged into the lower one?

Yes, it blocks most any plug. I dont understand why companies design plugs and power bricks without the clearance in mind. Also, it feed the cable from the bottom, so if you have trim that protrudes from the wall, or a low to the floor plug you might be forced to put it in the top plug of the outlet, like I have, which completely blocks the other outlet. I wish the Ethernet cable plug into the side of the unit. Bad design all around.

Brand	NETGEAR
Product Dimensions	7.11 x 13.36 x 3.78 cm; 684.92 g
Item model number	PLP2000-100PAS
Manufacturer	Netgear
Colour	white
Voltage	100240 Volts
Operating System	Windows XP
Are Batteries Included	No
Item Weight	685 g
Guaranteed software updates until	unknown

NETGEAR Powerline Adapter 2000 Mbps (2) Gigabit Ethernet Ports with Passthrough + Extra Outlet (PLP2000)

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