Auto Rental from SIXT - Phone Charging Expectations

It's a roll of the dice., and nothing is 100% assured, but these days it's very likely that there will be a standard USB charging port in the car (maybe even more than one of them), IME it's usually the classic USB "A" (rectangular) port that everyone is familiar with. I would bring a standard charging cable, maybe an adapter or two depending on your device(s). It's unusual (but still possible) to find either a round old DC port (aka cigarette lighter), or no port at all?...that would be rare (higher chances if you're renting from a small, local outfit and/or in some obscure backwater...) but Sixt in Slovenia is more likely to have new or new-ish cars equipped with ports and maybe even carplay. But it's not guaranteed.

I rent cars overseas all the time and can't remember the last time my car didn't have at least one standard USB power port.

Don't forget to bring a phone-mount for the car. Those are rarely (almost never) included.

I brought all of the above for France including an USB-A and USB-C because you just never know. I think ultimately we had Apple Car Play. It's such a roll of the dice.

My experience earlier this year ( domestically) was that the Mazda I got had only USB-C ports. No standard USB, nor a cigarette lighter plug.
Had to buy an adapter to be able to use my standard USB plug devices in the car.

What kind of plug you get is dependent on what car you get.

You might also want to take a USB-C to C cable. The car I had in Italy last year had both A and C ports. Remember that the European Union specified the USB-C as the standard connector. If the phone doesn’t connect to the infotainment system of the vehicle, just use the phone for GPS and definitely take a phone mount.

My last several cars have had USB-C. I regularly use Apple Play - can’t quite remember the last time it wouldn’t work.