Your brownout or blackout statement may be right or not (note I support getting a UPS, too) but you’re still missing the point.
OH by no means can be compared to OpenSprinkler or similar lightweight SD write loads as @rlkoshak showed.
Point is you wrote this in an openHAB forum where a lot of people use Raspis running on SD, and it is highly dangerous to make them believe that all they need is a UPS.
But they also need to take complementary measures to protect them from having their OH servers crash every few months, see this standard post.
