Most I am familiar with are full wave bridge rectifiers or at least full wave. If you are seeing half cycle on a scope I would suggest an open diode.
Today many are better technology and lighter and more efficient.
Old converters could be anything, but I doubt single wave since the filters would be more expensive than the other diode. The tapped transformer more than the next two diodes as well.
When I posted I had a senior moment and forgot that the new technology is switching power supplies that do away with a lot of the weight
and cost of the old time converters.
The Progressive Dynamics is most likely one of these since it is very light for the power output.
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