told to me and
emperical evidence agrees) that it is the only
difference
between the various grades (ie spec & hospital) of devices.
IIRC, hospital grade receptacles must exert more pressure to prevent
sparks, which would be a bad thing to have around oxygen tanks.
Could be ground issues, I use hospital grade AC cords and they have a funny
link in the ground wire as well and clear plastic so I can see its status.