[onetwentythree]

Yes. Power supplies up to 60VDC are typically designed to fall under SELV and are considered intrinsically safe. SELV requires isolation and a single fault tolerant design. Here is some additional info:

https://www.edn.com/what-does-selv-mean-for-power-supplies/

I doubt the USB-C power negotiation feature is specifically a safety function, but as other comments have pointed out it makes the system even safer.

I haven’t looked at the spec, but I wonder if there is any functionality that prevents a power supply from applying 48V all the time. i.e. is it possible to deliver a functional charger that is not SELV and has no power negotiation?

[detaro]

it's not, since a device has no obligation to be able to handle 48V input.