The price is right but it may take a week or more to get it.
Specs say it is adjustable in the range of 3.7 to 4.3 and is rated 40 amps at 4 volts. Not as small as a wall wart but it hits your target voltage and again one hell of a price from a good manf.
Just use a common 5 volt power adapter with the appropriate size resistor for each flashlight.
Also consider that flashlights are designed for maximum brightness and not long service life so don't expect them to run for all that long before the LED chips start to degrade and dim considerably.