Plugged laptop into my USB-C dock as I often do, but the two external screens were mirrored. I tried everything - replugging, rebooting, downgrading the kernel. The OS was only seeing one screen. Tried replugging everything into the dock. Finally I unplugged absolutely everything, even from the wall, replugged it and it worked perfectly. So I conclude it was electrical interference. Now I'm not so sure about USB-C "power going both ways".
@alex
Don't forget, that the connector you have just used is the legally approved connector of the future.
*legally required
@alex
Oh... I thought you have blocked me months ago 
I just hate the idea based on how inflexible the law tends to be. If a better cable got announced tomorrow, we will have to wait another decade before EU will get to changing the law again to allow it.
True, but I do like that the EU made Apple cut its bullshit, even if it sets a bad precedent.
@alex
Also, I would add, do you remember mini USB? That cable appeared and got discontinued almost instantly.
That is the freedom, that this kind of law would not allow to repeat. Nah, I want the best, no matter if the law makers are ready.