Paydirt! I stumbled across a {sort of “official” AND on-line} chart with the common lower US voltages and their acceptable ranges. The big kahoona is ANSI C84.1-1995, but you have to pay money for a copy of that one.
http://www.ari.org/std/individual/110-2002.pdf page 6.
[Sven, your bottom "crowfoot" picture is officially rated “125/250-volt non-grounding," but for window air-conditioning circuits the third blade was once common for grounding 230V metal appliance frames.]
For the sake of other readers, Sven’s top two pics are the current “code” versions, termed 250-volt [not 125/250] grounding style. Note that the “T-slot” opening in the second photo is to allow insertion of 15- or 20-ampere plugs. {The plug pins are not T-shaped, but a flat blade either positioned vertically for 20 amp, and horizontally for 15 amp.}
