OK, so I know about the various horrible things that vehicle supplies can do. (Although I believe that newer cars are probably a lot better). I tried one 'automotive' IC, but it had a voltage bump on startup, soI just went with my own battery supply for now.
Then I wondered about USB chargers as a source. They are fairly popular, but I wonder if they do supply a constant 5v or if they are depending on having a reasonably stout battery as a load.