The lab gets shrunk and get reversed on the effect. I am wondering, where is the power supply coming from?
The power for the lab does indeed come from Dr.Pym's fantastic particles but less so on them making a generator. It's actually powered on batteries, or a single battery to be precise.
Briefly seen in the trailer, and in the backgrounds during the movie, there is a massive Duracell battery that Hank is using as the power source for his entire lab. In fact, if you pay attention to the background there a number of different items he uses as enlarged tools throughout the movie such as LEGOs, erector sets, snackbag clips and more.
Hank Pym is a celebrated scientist with considerable knowledge in particle-physics. Perhaps even using the pym-particle technology he can produce small and effective power generators.
Even assuming there is no direct application of the pym-particle to power generation, there's no reason why the lab, which is disguised as a fairly large office building, couldn't include a large diesel powered generator and fuel tanks.
Well, the movie coughs and mumbles "Pym particles" whenever someone asks about anything physics related. Is mass conserved or not when things shrink or get enlarged? Depends on what the plot needs at that moment. What about momentum? Depends on what the plot needs at that moment. Energy? You know it.
So the power source for the lab would be (depending on your preferences) one of the following:
- A pym particle energy generator (probably the intended device)
- Suspension of disbelief
- Plot magic