I found these 5V chargers at Dollar Tree to work for me when powering an Wemos ESP82166.
Pretty easy to find and cheap.
Start with the USB part and remove that one screw.
Should be come apart pretty easily.
On the 12V side firmly grip the cone and rotate it off.
A bunch of pieces should come out. They are not needed.
At this point the external shell should easily split apart. Remove that horseshoe shaped spring.
You should desolder the little tab on the front.
Here are the where the 12v inputs and ground should go. The solder comes off surprisingly easily.
Here are the 12V leads soldered on.
Electrical or duct tape should hold the ground lead securely.
Seems like a lot of work, but it is cheap and small 5V source for a wemos that itself has a built in regulator.