I think maybe, definitely NOT do this. Measurement shows the provided adapter/charge controller ranges 4.0 to 4.3 v and current at 200-220 mA.
Plugging into an un charge controlled 5 v 1A power supply immediately drives the current to 1.1 A.
Certainly leading to overheating, possibly venting and leaking, venting leaking and lithium fire, rapid venting, explosion, and then fire. Pick your poison.
Although the adapter is rated at 500 mA; when connected to a 1 A USB load tester it supplies only 250ma.
So, someone tell me, where is the charge controller, in the flashlight or in the wal wart?
FINAL HOPEFUL UPDATE
In a disturbing development after charging at 4 v for 180 mAH the voltage across it dropped to 3.0 and it started getting hot, AND the flashlight is only intermittently shining any light at all.