External flash units, often called strobes, connect to the camera using a PC connector cord.
This connection was designed by the Prontor-Compur shutter works in Germany – hence the name “PC”. Has nothing to do with Personal Computers or Political Correctness.
Most cameras today use a hot shoe to hold a separate flash. A hot shoe to PC adapter lets you plug in the PC cord to trigger the flash.
This causes one of the most frequent fails for photo booth operators – a bad connection. You should always carry an extra adapter and an extra cord.
Sometimes the cord tip fits loosely into the adapter, causing an intermittent failure.
Tighten it by gently squeezing the tip with a pliers. Just a smidge. You want the cord to fit tightly but not require too much effort.