Later in the conversation someone links to a Twitter exchange which I found quite interesting:
> (@m_ou_se) I just tried to charge my phone by connecting it to my laptop (with USB-C), but instead of my phone, my laptop started getting charged, quickly draining my phone's battery. Uh, what.
> (@Gankra_) in case you aren't familiar: there was a semantic function of asymmetric usb cables that symmetric usb-C has broken. to "fix" this, each device picks a number for how subby it is, and the less subby one is the dom and charges the sub. these numbers can be surprising.
> (@m_ou_se) After some experimenting, I concluded that Dell laptops are the most powerful USB-C PD doms followed by ThinkPads, while phones and MacBooks are (equally) subby. Connecting phones and MacBooks with each other results in a switch fight.
> (@m_ou_se) I just tried to charge my phone by connecting it to my laptop (with USB-C), but instead of my phone, my laptop started getting charged, quickly draining my phone's battery. Uh, what.
> (@Gankra_) in case you aren't familiar: there was a semantic function of asymmetric usb cables that symmetric usb-C has broken. to "fix" this, each device picks a number for how subby it is, and the less subby one is the dom and charges the sub. these numbers can be surprising.
> (@m_ou_se) After some experimenting, I concluded that Dell laptops are the most powerful USB-C PD doms followed by ThinkPads, while phones and MacBooks are (equally) subby. Connecting phones and MacBooks with each other results in a switch fight.
(https://twitter.com/m_ou_se/status/1502664680602492933)