It's more efficient to use many 90ish% efficient switch modes supplies for AC to low voltage DC than to run 12/5v all over the place because the resistance of t

It's more efficient to use many 90ish% efficient switch modes supplies for AC to low voltage DC than to run 12/5v all over the place because the resistance of those wires makes any sort of distance inefficient as all hell. Also you'd end up needing hella fat wires; if you want to run 12v everywhere but say your cumulative prospective 12v consumption is like 2kW then you'd need wires for the trunk lines that are like 20mm diameter! (like 160A)