My S10e has started charging in 'Safe Mode' when being charged from my PC (and, apparently, slower) - this has only started recently. It still charges normally via the Samsung wall charger.
I can't get any sense out of Samsung as to why this has started happening, let alone how to stop it! I also find it difficult to accept their line that (slow) charging from a computer could 'damage' the battery - I always understood that slow charging equals less heat, less damage!
I've seen some other comments about upgrades affecting charging performance and wonder if that might be the reason behind this?
Any comments/help would be much appreciated!
I now think that you're right in that this isn't 'Safe Mode' at all, but the mere appearance of this symbol (with it's yellow triangle) definately seems to be a warning of some kind to my mind - (perhaps that the charging current is lower than it expects?).
Unlike your S21U, my symbol DOESN'T disappear after a few minutes (and you said that your wife's S10 doesn't show it at all!) - I'm also pretty sure that the appearance of this symbol is a recent delvelopment in my case - perhaps the result of an upgrade?!
I'm not sure where the "isn't turning off" came from?!
When I connect to the computer (with the phone turned "off"), up comes the rotating green circle (around the existing percentage charge), together with the warning triangle/plug symbols. This screen vanishes after a few seconds under any circumstances (screen/battery saving?). A short press on the power button makes no difference at all (except to restore the screen brightness after it's dimmed) or to simply restore this screen after it has gone totally blank.
If I connect to the computer with the phone already turned "on", I don't get the warning symbols in question at all - just the little percentage figure and how long "until full" in white at the bottom of the screen. A short 'power' press then just takes me to the phones normal opening screen.