The electricity supply is 220 volt AC, 50 Hz.  European style 2-(round) pin plugs are the standard but it is best to carry the full gamut of European and North American plug adapters if traveling through other countries. A very convenient information on worldwide adapters and plugs is the website http://www.interpower.com/ic/guide.htm. You will find pictures with each kind of socket worldwide under the various countries, Mongolia included. In the interior, there is usually no electricity.  Fuel generators are sometimes in use.