Does converting power from AC to DC vary depending on the device?

Yes. In the case of day-to-day portable electronic devices (e.g. mobile phones), a converter is usually placed inside the plug. In the case of electric vehicles, this converter is inside the car. In the case of DC chargers (for fast charging of electric vehicles) this converter can be found inside the charger itself. In this case, the converter inside the charger takes care of the conversion. As a result, DC chargers are usually larger (and more expensive). Power always needs to be converted from AC to DC when charging an electric vehicle, the technical difference between AC charging and DC charging is whether the power gets converted outside or inside the vehicle.