Amazingly enough, I have both of those same cards in the same capacities in other cameras, though I currently have a SanDisk High Endurance in my A129. Because I want to find out about any problems before I start relying upon them, I do a 10x full disk test write burn-in test on every new storage card that I buy, and have had surprisingly few failures -- and none of these brand/model combinations have ever presented any speed problems or read verification errors. While my sample size is not large enough to reach any conclusions with absolute certainty, given what I have observed I would tend to think that the maximum writing speeds on these storage cards are likely to be higher than the throughput of processor/storage controller/bus combination in the A129. (Though this is admittedly untested.)
While it is probably likely that the Samsung EVO Select 256GB may fail prior to a Samsung Pro Endurance 256GB if the same volume of data is written to them at the same rate, the Samsung EVO Select 256GB may just last as long as the Samsung Pro Endurance 128GB in those same circumstances. But given that all of our collective experiences is highly positive for both of these brand/model cards, I think it is fair to assume that the memory cards are not causing this particular problem. And let's face it -- we already know the likely cause, and blaming the memory cards is a dodge (though possibly unintentional, as faulty memory cards are an often cause of many dashcam recording problems).
If either of you you are willing to near certainly eliminate the memory card as a contributor to problem, a testing utility like h2testw can produce the test results needed to confirm that the specific instances of your cards are not failing in some way.
As for the power converter/adapter possibly causing the problem, they are both using parts supplied by the manufacturer of the camera -- and one of which is saddled with an additional design/manufacturing defect causing many A129 users to endure some audible circuit whine to boot.