As with most places in the world Namibia has an electricity grid. It seems to surprise many people that our electricity supply is both stable and reliable, well in the major centers at least. In cities and towns such as Windhoek, Swakopmund, Walvis Bay & Tsumeb you can be assured of a constant supply of as much electricity as your heart desires.
In more rural areas (and we're thinking especially of farms and lodges) electricity may be slightly harder to come by. However the good news is that pretty much anywhere you will be staying will have made some attempt to provide you with electricity either via solar panels or generators. This means you may not have 24 hour electricity and also using some appliances (eg hairdryers) may not be practical.
In Namibia we use 220 volt electricity and for some reason we have adopted the South African system of electric adapters. Most plugs have three round pins but some plugs with two smaller pins are also found on appliances. US-made appliances may need a transformer.
"Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking.", Dave Barry