TBH, I have dozens of D1 Mini’s and D1 Mini Pro’s, most of which are deployed in hardware that is either in Spain or here at home in inaccessible locations.
Looking at the ones I have in my spares box and kicking around on my bench, they have a mixture of voltage regulator chips marked:
WJ=U1A
4A2D
4B2K
S2TG
As I’ve said, I’ve never had any issues with devices going offline unexpectedly. Looking through the uptimes of my Wemos based devices here at home, all are reporting that they’ve been up for 67 days, and that would have coincided with me turning-off the mains power to do some electrical work. I typically see much longer uptimes that that.
Pete.