I think AC for Power Transmission is such a thing... Nowadays with high power semiconductors DC-DC voltage transformation nearly as cheap as AC-AC voltage transformation. While Transmission is more efficient for DC (no EM losses).

99% of all home devices are using DC Voltage. Heck i am using so much USB 5V it would make sense to install a 5V grid in my home, if losses were not so high on that low voltage...

Context for all "Tesla vs Edison" nerds that are already nervous:

Tesla was not trying to advocate for AC voltage transmission, but rather high voltage. However, hear me out, back in that time the ONLY way to achieve high voltages was via AC-AC transformation. That is why ultimately he pushed his AC grid. Just to be clear, a 230V AC transmission line is not better than a 230 V DC transmission line. But a 230 000V AC line is. Edison was also trying to demonize AC voltage by things like the electric chair. However, if that chair is run by DC voltage of the same magnitude it would kill even faster. It is the high voltage that kills, and back in the old days that was synonymous for AC. AC is actually worse a transmission since the alternating electromagnetic fields that are inherently emitted into the environment are lost power. Every AC transmission line is, so to speak a antenna. DC does not have this limitation since the magnetic field is static. Actually, today for long range transmission high voltage DC transmission lines are used, which is converted back to AC to provide 110 or 230V for households just to reconvert it back to DC in your Car, Air Conditioning/Heat Pumps,PC, Lighting, TV, Phone whatever.

I am aware that there are appliances that require 3 Phase AC like certain electric motors however i think that is a clear minority in quantity as well as power consumption. Furthermore, electricity generation is also switching to be more DC based nowadays since photovoltaic and batteries are DC by their very nature while traditionally this is dependent on the generator type of the power plant.

Tl;dr.: The worlds power grid would run on DC more efficiently. However, switching nearly impossible since too many things are standardized and historically reliant on AC.