Original post by: a finder ,
I had the red x problem with my tab 12.2 even though I was using original/correct 5.3 volt charger and cable (compared to Galaxy Note 4's 5.0 volt charger). The solution that worked for me; With tablet on and unplugged, hold down power button briefly enough (so not to turn off tablet) to plug in cable, then release power button. No red X. The bummer part is that I need to do that every time I want to plug in power while using. Luckily a very simple solution, but it would be nice if it would just work plugging it in. For me... it use to be able to charge just plugging in, not sure what made that change.