How to you measure whether the output voltage is fluctuating? I measured the PS that came with mine and it was 15.1 every time. Forgive the noob question, but would that voltage output change when plugged into the device?
What Amir said is right: unregulated power supplies will have voltage fluctuations with load (i.e. current draw).
But, your
mains voltage (i.e. your home's AC outlet) can also fluctuate. I'm not sure about unregulated switch-mode supplies, but at least for traditional transformer + rectifier, AC to DC supplies, the output voltage is proportional to the input voltage (i.e. mains voltage), and that can and does go up and down quite a bit. I have an uninterruptable power supply (UPS) which allows me to query the mains voltage it's seeing. I log this. Over the last year, my mains voltage has swung between 105V and 130V, which is about 20% variance.
If you assume my mains power fluctuation is typical (20%), then a simple transformer+rectifier power supply targeting 15V would actually give 12v to 18v in practice. The gap is actually bigger, once you factor in Amir's comment, that the voltage is likely to drop even further under load.
Would that mean it's better theoretically to have a lower voltage power supply that reliable outputs, say 12V -14V, instead of a constant 15V for the longevity of the device? I ask because I just bought a meanwell 15V 1.66A powersupply after hearing stories on here of bad ones potentially causing issues. I could still return it and get a lower voltage one.
I would say yes to this if indeed my speculation is correct, that powering the DX3 Pro with 12V is sufficient. But, as that's speculation, without getting confirmation from Topping directly, best is to use 15V to be on the safe side. (Having said that, again, if my guess is correct, a 12v supply will generate less heat within the DX3 Pro compared to a 15v supply. And lower heat generally means greater longevity. However, Amir showed in his thermal analysis that even at 15v supply, all the components are well within their safe temperature range. So while theoretical longevity could be increased, in practical terms, I highly doubt it matters.)