So originally I had a s23 with slow charging issues after 3 weeks .seeing as I was getting no where with Samsung I bought a s9 to get me by. Now after 2 months this has started to slow charge. Surely something is up?! Is samsjngs software causing this or is could it be the car charger that has done something to the phone. I just find this strange .as all chargers are fine with another phone as it fast charges or charges at normal speed when plugged in the car.
I think because of this whole charging issue i will be leaving Samsung as this is not a isolated case
Could possibly be the car that appears to make have issues, as you say the chargers are fine with other phones. The S9 is getting quite old as well now, probably not getting anymore software updates too.
Fast charging with Samsung devices can be oddly specific about which cables and chargers you use. They even vary from each Samsung device. But the basic rule is, make sure the charger supports Quick charge 2.0 or PD 2.0+ and you should be good for fast charging.