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Don’t Let Anyone Take Away Your Big Box of Cables - Jim Nielsen’s Blog
(blog.jim-nielsen.com)
This is a most excellent place for technology news and articles.
19.5v is pretty common for stuff that needs more power, but I'd bet there's some threshold at 20v that means a device is no longer "low voltage".
But AC? Are you sure? That would be exceedingly unusual.
I think it was for a printer