I'd argue it's not really DRM, it's more like device identification. Nearly all modern laptop power supplies do this in some way. HP and Lenovo ones use a resistor on the extra pin, while Dell has put a 1-wire memory chip.
The main reason for this is so that different wattage power supplies can be used with the same connector. The laptop determines the power supply type to see if it can safely draw its full load.
USB-C takes this one step further by having a full negotiation process before supplying any of a number of voltage / wattage levels.
> I'd argue it's not really DRM, it's more like device identification.
I suppose the key question is: Does it identify the device and then decide not to work with non-Dell devices? It's fine to read required information, but unnecessarily constraining what happens based on that information brings it back to DRM.
It's not an open standard so this isn't really meaningful. The data has to be formatted a specific way, the Dell way that is, but it's not signed or anything.
The charger is just letting the load side know what it can supply... There are tons of cheap charges that are specified to supply 65 watts but will happily provide more than that until they melt or light the floor on fire..
The power supply is "constant current, constant voltage" - ie. it is 19 volts for all currents under 3 amps, but if you try to exceed 3 amps, it will supply exactly 3 amps at whatever voltage that works out to.
The benefit of this scheme is it's super easy to implement on both sides, and fully universal - the device just keeps increasing the current draw till the voltage starts to drop, and it then knows it's hit the limit. The device doesn't need any kind of logic at all - a dumb light bulb will either work if there is enough power, or not work if there isn't, but nothing will get damaged.
It's also compatible with Y splitters - so you can plug in two laptops to the supply, with no extra electronics, and both can share the power. (there is no guarantee of even power splitting tho!)
A big benefit is the power supply can have fully variable capabilities - for example, most power supplies are thermal limited, and on a cold day it could offer slightly more current to charge your battery slightly faster - all without any digital logic, protocols, or anything manufacturer specific.
Anything more complex with sense resistors, ID chips, extra wires, etc. just costs more, and provides less utility, and almost looks like a deliberate attempt to reduce compatibility and increase sales of chargers.
The main reason for this is so that different wattage power supplies can be used with the same connector. The laptop determines the power supply type to see if it can safely draw its full load.
USB-C takes this one step further by having a full negotiation process before supplying any of a number of voltage / wattage levels.