To a degree, this is why the Switch-mode Power supply has won out over the Linear type.
With a higher frequency, there is less transformer.
However, DC, within buildings, is a totally different kettle of fish.
Most places are designed to have AC switching in them, the difference being the distance between the contacts and the speed at which they close (or more importantly) open.
AC has a natural current zero, twice per cycle.
DC has none of this.
I have heard of where a bulb has blown, that the arc has travelled back down the wiring to the switch and had the switch not been opened, the wiring coulkd have burned further.
DC needs a lot heavier contacts and quicker opening than AC.
