As I have often stated, NEMA configurations aren't that old.
Prior to NEMA, (say pre-1970), there were a variety of plugs made. Not all of these patterns were adopted by NEMA- the three prong dryer plug, and the 30 amp, 125 volt RV plug among them.
The point is, many of these older styles carried dual ratings, for widely differing applications. It is very possible the plug this guy is describing had both a DC and differing AC rating.
The NEC does not require you to use NEMA configurations. There are still a multitude of non-NEMA patterns in use- just look at the back of your computer monitor!
Now for an editorial comment: Already I've had to "save the day" for folks who wanted 'alternative power,' but were given poor advice (and incompetent engineering) by the vendor. I have seen one licensed EC go bust, in part because such a job put him in way over his level of expertise.
Alternative power- be it solar cells, wind power, generators, or UPS systems, will become a larger part of our trade. Many times, you will have to sort out someone else's mess first. Start learning NOW, so you can 'save the day' yourself.
