I don't think the meter would work, he's measuring a c voltage.  There was
a discussion a while back on the handyman list about how to build one of
these things.  I think you could actually check it with a meter--come to
think of it.  Just tried it with a meter and it works...  Hold the plug in,
or rather picture it so the ground hole is to the bottom.  The left hand
slot,  the long one is ground.  The right hand one, the shorter of the
two,, is plus.  Between the two slots, you should read 120 v a c.  You
should also read voltage between right hand or plus terminal and the
ground hole.  If you measure between the ground hole and the left hand or
minus slot, you should see very little difference in voltage, as these
are basically at ground potential.
Hope this helps and makes sense.
73s
Butch Bussen
wa0vjr