Four Essex County men have been accused by federal authorities of robbing a United States Postal Service employee at gunpoint last year, U.S. District Attorney Philip R. Sellinger announced Wednesday. Troy D. Corbett Jr., 28, Dyshawn Williams, 28, and Antwuan Brown, 24, all of Newark were charged with conspiracy to commit Hobbs Act robbery. Karieem Stamps, 25, also of Newark was charged with wire fraud and aggravated identity theft. Brown was also charged with wire fraud and identify theft. Prosecutors accused the men of holding a postal employee at gunpoint while robbing the person of a cellp…