As Breaktru mentioned, recheck your circuit and if you find nothing wrong with it, check output with a decent multi-meter. Good ones have pretty sophisticated averaging circuits to deal with voltages that may not be perfectly DC which is the case for the output of a power converter. Higher end meters use "true RMS" which takes it a step further properly accounting for non-DC characteristics in terms of their RMS effects.
The output of a converter is essentially DC, but there's an amount of ripple in it. It varies depending on the converter and power demand. There can be an amount of variation depending on load. You should check voltage while the converter is powering something, doesn't necessarily have to be an atomizer, a load a tenth or two of a Watt will do.
Those meters you screw inline with the atomizer have no averaging circuitry and can fail to properly read voltages that are not perfectly stable. Even some electronic components can have problems with the output from a power converter. I came across a linear regulator that would simply not run from the output of my converter, though it was fine when powered by my DC power supply which has pretty much zero voltage ripple.
Adding output capacitors can reduce ripple quite a bit. That may be an option if that's the problem and you want to eliminate it. Voltage ripple has zero effect on atomizer performance so it's normally not something you have to do.
