s9 plus fast charging

disabled? check your charger or try a different fast charger, you cant disable the speed of your phone recieving charge, that only depends on the charger and the phone's hardware. people always tend to blame everything on the last update they had

pawtatuh, agree with you. also i dont think that a software can make an effect to hardware

even in online they said the same

Goto Settings --> Device Care --> Select Battery --> Select Three Dot icon in Top right corner --> Check Fast cable Charging is enabled

then try checking with another fast charging cable or charger... if it works then it urs might be faulty

if it didnt work try factory reset once and check

Visit a Samsung customer service center... That would be the final thing to do... If it's in warranty you wont be charged for any service...