Well, there are lots of things that can over-rate a power supply. For example, using a 5v regulator that peaks at 1A, but not heat sinking it. Sure, it could deliver 1A in a perfect heat-sinked-world, but in fact is going into thermal shutdown at 500mA, for example.
As a general engineering rule of thumb, you de-rate at least 50%. Then marketing gets a hold of it, someone leaks that there's really a larger regulator in it and BOOM! Suddenly it's over-rated.
If I build a device requiring 1A, I ship it with a 2-2.5A power supply. Another advantage to that is that the power supply isn't being driven hard, and will last substantially longer.
Cheap filter capacitors can also de-rate the supply. Wire that's too small. Traces that are too thin. The list goes on and on.
A lot of this stuff coming out of China starts off great, but when it comes time for them to deliver a million of them they shave the copper so thin that you end-up recalling all of them (ouch).
I've found that you have to take the order in small batches and sample repeatedly. Don't be afraid to have your dog hike his leg on it at the dock and kick it back over the rail again. Anyway, beside the point. Likely your 1A supply is 1A in a perfect world but probably goes into thermal shutdown at something around half of that. Your atomizer heats up, the resistance drops, and you peak out at 800mA and the thing shuts down... Without having it in my lab, that'd be my first guess.
