said by RickStep: Notice numbers in some APC salestools. How many volts did 1970 electronics withstand without damage. 120 volt electronics could withstand 600 volts. Today's electronics are even more robust. Why does a 120 volt UPS even output 270 volt spikes. Because electronics even in the APC citation says 600 volts without damage.
Ive listed below 3 publications from American Power Conversion. The publications cover much of what has been discussed here.