OK, so as I'm currently waiting for my first tesla I'm trying to understand what this means exactly.
Somehow the 14-50 plug became known as the NEMA plug but this is not correct. All power plugs used in North America are National Electrical Manufacturers Association (NEMA) plugs. The Tesla Gen2 Mobile Connector accepts a range of 120V and 240V NEMA power plug adapters. You select the specific power plug adapter to match your receptacle when charging.
When you charge a Tesla vehicle using either the Tesla Wall Connector, Tesla Mobile Connector or Tesla Supercharger you don't need to use an adapter.
When you charge a Tesla vehicle using a non-Tesla charging station that has a J1772 charging connector (as found on most public Level 2 charging stations) you need to use the Tesla SAE J1772 adapter that comes with the Tesla vehicle. This small part can also be purchased for $50 from the Tesla online store if you lose it or want to keep one at home (because you use a non-Tesla charging station at home) and one in the vehicle.
To charge a Tesla vehicle using a DC Fast Charger station that has a CHAdeMO charging connector you need to use the Tesla CHAdeMO adapter (no longer sold.) Nissan, a few other EV manufacturers that previously used the CHAdeMO charging connector for EVs sold in North America are now moving away from CHAdeMO as a charging standard in the US (CHAdeMo is still very popular in Asia.)
To charge a Tesla vehicle using a DC Fast Charger that has a combined charging system (CCS) charging connector you need a Tesla CCS adapter (this adapter is still coming to the US, currently available in South Korea.) Note that the CCS charging standard in the US is different from the CCS standard used in the UK and Europe. Tesla vehicles sold in the UK and Europe use this non-US version of the CCS charging connector.
For charging the Tesla vehicle at home you can use either the Tesla Mobile Connector or the Tesla Wall Connector. The Tesla Mobile Connector is no longer included so you would have to purchase this from Tesla for $275 for the kit that comes with the standard NEMA 5-15 plug adapter (fits the standard 120V/15 amp receptacle found in the home.) Additional power plug adapters are available from Tesla, cost between $35 and 45$ each.
The Tesla Wall Connector currently costs $495 US and is designed to be hard wired (no plug) into any 120V or 240V charging circuit that is rated between 15 amps and 60 amps. At first glance the Wall Connector may appear to be more expensive than the Mobile Connector but when you add up the cost of all of the additional components needed to use the Tesla Mobile Connector with, for example, the NEMA 14-50 receptacle the Wall Connector is actually less expensive than using the Mobile Connector with a NEMA 14-50 receptacle now that you have to purchase the Mobile Connector.