I don't know anything about Apple world... Our customer did have a Macbook (I think) and now he did switch to an iMac (I think with El Capitan?).
A simple barcode reader USB did work on old Mac. It did "beep" and it did write the scanned number properly on the screen.
With new iMac now the barcode reader does "beep" but it doesn't write anymore on the screen (on an Excel / Notepad / Browser etc etc etc).
Reading on the internet seems a well known bug of El Capitan.
Someone has tested some USB barcode reader and it works on El Capitan? For now not a big problem the cost... Or do you have a workaround?