[lovemenot]

>> With DC, nothing is really at the same voltage, so you need DC-DC converters all over anyway,

This may be the case now, but it's just through historical lack of standardisation, resulting from AC having been the one true standard. It's not inherent to DC.

USB PD is attempting to address this issue. It is standardising voltages for DC-powered devices.

[SilverRed]

Even internally there is no standard. You may put 12V in your user facing input and the device then splits that in to 12v, 5v, 3.5v for all the different components which run at different voltages.

[Robotbeat]

But internally, devices operate at different voltages due to fundamental differences in required voltages for their transistors, LEDs, battery cells of different chemistry and charge state, etc. There’s not much getting around it in a strict sense, although standardization can help.

[bluGill]

USB PD works because they can assume very short distances. It wouldn't work for anything longer than a few meters, and it isn't clear you can safely scale it up to longer distances or higher voltages.

[rini17]

There are inherent factors, though.

1. Any time you mix motors and electronics, motors produce brownouts and spikes which can cause directly connected electronics to malfunction. DC-DC converter mitigates that. LEDs are particularly prone to overload with just minute increase in voltage and dim/flicker with decrease.

Not inherent to DC but same thing happens with poorly designed appliances that emit RF which then interferes with everything connected to the circuit.

2. Voltages. You can't standardize electronics power supply to 12V because semiconductors are most efficient at lower voltage, which depends on particular technology.