doesn't really matter if it's marked "AC" most of those supplies are isolated input anyways.
if you really want to get uppity about the voltage input though, you can take apart the supply and see where the screw terminals lead to... the one with the fuse on it TECHNICALLY should be the live wire whilst the other is neutral. but in all honesty, it doesn't really matter if it's generically marked.
if it mattered much (due to regulations or a particular setup is used where neutral is tied to chassis ground), it would be marked L and N