It's not a question of chargers: It's a question of laptops in standby.
The historical design intent of USB is that, even when your laptop is in standby it still powers devices like your keyboard (so you can press keys to wake it up) and in exchange, devices promise to consume less than 2.5 milliamps (12.5 milliwatts) until they've negotiated permission to draw more from the host. After all, it'd suck if your laptop battery was going down noticeably even when the laptop was in standby.
Of course, loads of vendors of cheap devices ignore this - the makers of a $5 rechargeable bike light or USB fan aren't going to put in the components needed to negotiate charging speed. But in principle if you made a USB cable with only the power pins connected, compliant devices should only charge exceptionally slowly, if at all.
(Wall chargers, instead of enumerating as a USB host to negotiate power, used to put a certain value of resistor across the data lines, to signal what current the device could draw - this hasn't always been standardised, which is why phones and USB chargers can be incompatible)
Sounds like historical revisionism. Power limiting is possible without negotiation. It's easiest, for me, to find references to the safety aspect more than anything else.
Note also a fair number of laptops (read: every one I have used and checked) use PS/2 internally because it is interrupt driven and even lower power than USB. There are also plenty of laptops that advertise high current phone charging while off, some of which do negotiation, some of which don't.
Yeah, USB is seldom inside laptops, but you might be interested to know that it is becoming increasingly common to see HID over IC2 [0] used inside of laptops instead of PS/2.
I've definitely seen it. Reusing HID is kind of clever, but the protocol is extremely bloated and hard to parse.
Ignoring that, I'm not sure it's an improvement. Most of the power savings is having the keyboard initiate an interruptible event to wake the computer. Interpreting HID like in USB means the keyboard can't wake the computer, the computer needs to remain on to service USB interrupt endpoints.
The historical design intent of USB is that, even when your laptop is in standby it still powers devices like your keyboard (so you can press keys to wake it up) and in exchange, devices promise to consume less than 2.5 milliamps (12.5 milliwatts) until they've negotiated permission to draw more from the host. After all, it'd suck if your laptop battery was going down noticeably even when the laptop was in standby.
Of course, loads of vendors of cheap devices ignore this - the makers of a $5 rechargeable bike light or USB fan aren't going to put in the components needed to negotiate charging speed. But in principle if you made a USB cable with only the power pins connected, compliant devices should only charge exceptionally slowly, if at all.
(Wall chargers, instead of enumerating as a USB host to negotiate power, used to put a certain value of resistor across the data lines, to signal what current the device could draw - this hasn't always been standardised, which is why phones and USB chargers can be incompatible)