My S9i with apw3++ has been fine with 248-252.  Mostly at 249-250. depending on time of day.

Last fall power company sank a new pole in front of house with new transformer to supply 2 new houses with a total of 5 houses supplied from the one.  Not sure once the new houses are occupied if I'll still be sitting at 250 or if I'll drop back closer to 240.

Until that first PSU problem was brought up with the input voltage, I was understanding that most everything was assumed to operate in that 220-260 unless specifically stated otherwise.  (obviously I'm referring to 200+ circuits not 120 lines)

I'm not the OP but I appreciate the research and testing, so that I'll be be better informed and what I should do or what is not necessary when I upgrade to S15 and beyond.