Changing power supply
Unfortunately, my selfbuilt USB-power supply didn’t really survive very long. I probably could’ve put in a little more effort.
Well, whatever. I’ll just take this as an opportunity to switch to a what I think is a more reliable power source. I bought a step down converter which can convert from between 4-40V down to 1.25-30V. Since I got an input of 12V of the car and I need 5V for my Pi this fits alright. I chose the LM2596S which I got for 6€ off Amazon. Besides being powered via USB the Raspberry Pi may also be powered via GPIO. Since I didn’t want to cut any USB cable I just connected the Pi’s 5V pin to the switch directly which itself is connected to the converter.