I believe that the root of the question is essentially: "look! Cheap switchmode power supplies being produced in the millions for the LED lighting market! While they're supposed to be "constant current", don't they have a practical limit on output voltage that falls in the range needed at the input of an Arduino?"
Answer: maybe. But the cheap switchmode power supplies being produced by the millions for the cellphone/etc market are more appropriate and not that different in price. (although, the price goals of the supply for a $10 lightbulb are probably lower than the goals for the supply for a $100 cellphone/videogame/whatever.)