This paper presents a comparative efficiency study for the use of Direct Current (DC) and Alternating Current (AC) power in the residential distribution power system. The U.S. Residential Energy Splits data for year 2015 from 'Buildings Energy Data Book' has been used for modelling of residential buildings. Distribution system models have been made for both AC and DC powers. The system efficiency values have been tested for different cases. The AC system was found to be superior to DC with a minimum efficiency advantage of around 2% and a maximum of around 6%. Subsequently, the building air-conditioning loads were assumed to incorporate the modern concept of Variable Speed Drives (VSD) which Use an intermediate DC power stage. If the building power supply is DC rather than AC, then the intermediate AC/DC conversion stage may be avoided. Taking the air-conditioning as a DC load roughly doubles the DC power demand of building. The DC system showed slightly (around 1%) higher efficiency for the VSD air-conditioning case. Back in history, it was apparently the efficiency of power transfer that allowed AC to oust DC, and now, once again efficiency may be a decisive factor for the reignited competition between AC and DC. (C) 2016 Elsevier B.V. All rights reserved.