Hi I have the S10 + and found mine would only fast charge with the charger cable facing with the centre joint of the silver plug lead facing up. I also have a Samsung fast charger for my car and I never have a problem with it fast charging no matter which way I plug my phone into. I took my phone charger lead and tested it with my wall charger and phone and no problems so it clearly shows it's the charger lead at fault. The main obvious external difference between the two leads is the wall charger lead has a joint on one face of the charge plug whereas the car charger lead is seamless. It's still under warranty so I'm going to check with Samsung and get the lead replaced. As mentioned it could be an issue with the board but changing the cable seemed to work a treat for me.