Why wont my phone fast charge while on, but only when its off

[AC Question]

My phone as of late has trouble charging when its on, even when its in ultra power saving mode, it took 4 hours to get to 90% charge from almost dead. While its off it has no problem charging, so I feel its some of the 3rd party apps that I've downloaded but I dont know how to tell what is drawing all the power or whats stopping it from charging properly while being on.

I have a new samsung galaxy s7, fully updated