What scares me about the 'PC to household' flash cord is not that the photographer might make a mistake, but that someone else in the vicinity might make a mistake and plug your camera's PC sync socket into 120V power... what will that do to your camera?
I did a gig a few years ago which had an unmarked "special outlet" in the gymnasium wall for the floor buffer. Yup, it was a standard 120-volt NEMA 5-15 receptacle mis-wired for 240-volts. I plugged a rather nice Sennheiser RF receiver into it which did a bright flash and died (no universal power supply on this one). Ouch!