Knowledge about the value of used plug-in electric vehicles (PEVs), known as residual value, is critical for potential PEV purchasers, corporations, and governments who wish to consider the lifetime cost effectiveness of PEVs. We investigate the residual values of PEVs and compare them with those of other vehicle powertrain technologies using the "true market value" data from Edmunds.com, and considering U.S. federal incentives. We define the adjusted retention rate as the ratio between resale value and the manufacturer's suggested retail price, subtracting incentives. We develop statistical models to quantify the effects of powertrain technologies on residual value while controlling key factors, including vehicle size, brand, and market segments. We find that the long-range high-performance Tesla Model S holds value significantly better than any other vehicle type evaluated, including internal combustion engine vehicles. Hybrid electric vehicles and plug-in hybrid electric vehicles are comparable to one another. They hold slightly less value than internal combustion engine vehicles, but significantly more than short-range (< 125 miles) battery electric vehicles. However, short-range battery electric vehicles have a faster improvement in 3-year adjusted retention rate than any other powertrain technology from model year 2013-2014. The other factor that significantly influences adjusted retention rate is the home country of the vehicle manufacturer (e.g., United States, Japan, or Germany).