yeah,,, talk about a "hot chassis" device...
go with the suggestion of using a wall wart and regulating the output voltage to +5V, or get a 5V switching supply type wall wart. without the proper isolation between line (mains) voltage and the equipment you're adding or building, you are asking for trouble.
direct rectification and regulation may seem more efficient, but you end up with your output "ground" and +5 rails having the AC line voltage superimposed on them, which is very dangerous.