Hey there, so i recently just purchased a brand new Kess V3 and i am coming up to doing my first tune. I am not sure on how much power i should have to the battery. I know between 12-15v but not sure on the amperage. Is there a place i can look to find this information for when i do my tunes on customers cars. The car is a 2016 c200 W205.

TIA

This all depends on the car. Some Mercedes and also the EDC15P from 1.9tdi for example turn on the fan while flashing. So you power supply has to atleast deliver the current for the ECU + Ignition and the Fan.
It also depends on the reading time and battery. A car battery can provide hundreds of amps but only for a time period depending on the current. So with full car battery you dont need any power supply if you have short reading times.

Often, a 20A power supply is enough to stabilize the voltage of the battery suffiently for the reading/writing process.

If you haven't got a charger or its weak, then disconnect the E-Fan!