They did build it themselves and would know that they didn’t put in any capacitors, and yeah that was implying that the time travel field has some kind of capacitance.

The guy who wrote the movie is a mathematician who’s worked as a programmer, I studied years of electrical engineering before switching to computer science, and doing a masters in Material Engineering, Perhaps it’s you who didn’t understood something.

I looked up that part of the movie again to see exactly what you were talking about, they’re putting 24V into the machine, but the machine is using more than 24V, even after they unplug it the machine is still pulling more than 24V, perhaps you missed the point that they’re looking at a voltmeter (which is never shown on screen), which one of them suggest it’s busted and the other tells him that he’s tried 3 others. Or perhaps you missed the point that they built the machine, so they know what’s in there, they know the machine shouldn’t be doing that, so when they ask “What does that?” it means “What part of it does that?” or “What’s making it do that?” and not “What other things do that?”, the phrase can be interpreted both ways, but only one of them makes sense. The thing is that the movie doesn’t try to hold your hand and explain things in detail, the engineers talk like engineers, and that’s a very valid question in that situation, in fact I’ve asked that exact same question of several programs, it’s a very common question to ask when trying to understand what’s the cause for something.

And no, they’re not hinting at time travel there, in fact they go for days not knowing what the machine does, if you had bothered to keep watching you would know the process of them discovering time travel is a lot longer than that, that’s just the first mystery behavior from the box, which in fact has nothing to do with time travel but just an inherent way of how the box powers up and down, because it takes time to get into and out of the feedback loop.