It depends on the size. I think the small units can plug in a standard wall outlet. I think the larger ones get their power from the outside unit.

How about specifically the GREE NEO 18,000 BTU, 208-230V?

Even somewhat larger ones do NOT need to be plugged into an inside outlet. I think all electrical and cooling come from the condenser outside. BTW, we used 3 of them in an older home, and they worked great! But buy one from one of the better manufacturers, such as Mitsubishi.

Franco, yes!!!!

Is there only one indoor handling unit? Could there be more than one?

We are installing 2 indoor units.

I have a Gree system that heats/cools our basement and my husband's office. All needed wiring was run by the company that installed our system. There is wiring that runs from each head to the condenser unit and then the condenser is wired into our electrical panel. The unit you are looking at needs a breaker of 20 amps or greater. The heads are not and cannot be plug-n-play.

As to a Mitsubishi vs, Gree, Gree wins. I started out by asking for quotes for a Mitsubishi and every company I contacted (they all sold both brands and others) said Gree was better-price and performance. Here's a link for comparison Do a google search, there are more. Friends of ours own a restaurant in an historic building and they put in Mitsubishi. They are changing to Gree because of all the issues, the most important being it has not done a good job cooling-not fun in the hot and humid South.

One piece of advise, this is not a DIY project! Unless you have a certified electrician/HVAC friend who is doing it for you hire a good HVAC company.

Power goes to the outside unit and cable runs from there to the indoor unit. The latter does not require much power at all since the blower accounts for most of it and it is run by high efficiency ECM motor. Electrical code probably requires a disconnect near the indoor unit since line voltage is involved.