Imagine someone from the modern day somehow gets transported back in time around the same time of WW2 without warning ahead of time. He has with him a laptop, graphing calculator (and a hand full of backup batteries), a smart phone, and a digital watch. He wants to show of and use his technology, however, with the exception of possible the watch the all have limited battery life. I want to now how difficult will it be to find ways to charge these devices without damaging them safely?
For the sake of this question presume that the time traveler is not a hardware engineer, EE major, or otherwise has training that would help him to personally know how the electronic devices work or how to jerry rig power supplies himself. However, he has enough smarts and basic understanding of physics/electronics to have a vague idea that there could potentially be an issue with power that needs to be addressed.
He will also be quick to find those who recognize the importance of his hardware and would want to make sure they are safe, thus he will likely have the aid of people from the WW2 era who were trained in electrical engineering, hardware, and the like who would want to try to help him find a safe way to power these devices. These folks only have WW2 level knowledge though, and won't know specifically what type of power (voltage, current, fluctuation tolerance etc) the devices are configured to handle unless it's written on the device or they can reverse engineer it somehow. The only thing the traveler would likely be able to contribute is that wall sockets use AC power and batteries us DC, that's about the limit of his knowledge of specifics of the hardware.
So how hard will it be to jerry rig a safe power supply to charge his devices with the expertise available to him, and how likely is it that a miscalculation could accidentally damage or destroy the device in question?
I listed a bunch of standard electronic devices, but I don't expect any one answer to necessarily touch on all of them. I'm most interested in the laptop, but listed the rest both in case someone can provide feedback about them as well and because it's possible having them may allow more information to be derived before trying to rig the laptop power to ensure that one is safe.
I'm would be most interested in the situation in which the traveler does not have a charger for the laptop or cell phone available. However, if it turns out that having a charger makes it significantly safer (ie less likely to fry the hardware) it's okay to presume one or both exist.
Side question if anyone wants to answer, if the traveler didn't realize the risk how likely is it that he would destroy his hardware by trying to plug it in to outlets of the time?