Is it possible to connect the device Max-On-The-Go on eletric current the car?
Sure. Max On The Go accepts 10-24V DC input so can cope very well with being powered from in vehicle power supply.
How can I do that?
Do I need an another power supply?
If you are planning to connect it to a 12V socket, you can buy specific power supplies for this.
Most electronics stores should be selling these.
Here’s a photo:
If you want to connect it directly to the car battery, you could cut off the adapter on the standard power supply and strip it.
Or you could buy a power supply cable with a DC connector on one end and nothing on the other end.
Something like this: