> maybe in an ideal world, but this is absolutely not guaranteed at all. Some chargers only support the profiles they need and don't support the lower-voltage s

> maybe in an ideal world, but this is absolutely not guaranteed at all. Some chargers only support the profiles they need and don't support the lower-voltage standards in between. Even apple does this sometimes, in fact. Apple chargers follow the USB PD 2/3 spec which doesn’t include a 12v profile, which appeared in the original PD 1 spec. There’s good technical reasons for swapping the 12v profile for the the 15v profile, as 15v is far more useful for actually charging devices, but the rug pull spec change is certainly a pain in the arse. Good third party PD chargers will support all historical USB PD profiles, and Programable Power Supply (PPS), which allows a device to request any arbitrary voltage. But many first party charges seem to strictly implement only PD 2/3 with PPS occasionally. The USB forum have really messed up the labelling of these specs, but manufacturers like Apple are making perfectly compliant PD chargers, and implement everything USB PD 2/3 requires. > and yes, it should always work at the lowest-common-denominator standard, and there should be a profile for the base USB 5v 1A if nothing else but... not all devices do. Every USB charger does support 5v 1A. That’s what you get from a USB port before you start the USB PD handshake. The resistors on the USB-C CC pin indicate passively what the port will provide without a full PD negotiation. > Laptops often don't support lowest-common-denominator charging, for example. Of course laptops don’t support 5v 1A charging. It’s a complete waste of time. By the time the laptops power control electronics have finished converting into a useful voltage for internal power rails, you’ll have used up most of the 5W of power provided, and turned it into heat. There’s practically nothing useful a laptop can do with a 5v 1A supply. It’s not a meaningful amount of power, and it’s not a voltage that can be efficiently utilised for anything a laptop needs. USB-C and its associated standards are still in their infancy. For all its problems today, USB-C provides an excellence technical base, over the next decade we’ll see rapid convergence on a standard set of charging features and data features that will be implemented at scale with dirt cheap dedicated silicon. That final feature set will be far beyond anything we’ve had before, but we’re ultimately waiting for the standards to stabilise enough that the IC needed to implement the really useful features can become cheap and common.