Chargeable/ dynamo flashlight, needs a mains power source. Which power adapter do I use? I lost orig

Hi I have a flashlight which works rather well as a dynamo flashlight, but I would also like to be able to charge it with a mains power source. 
Problem is,  I lost the original power supply, and I don't know the polarity of the device, or which current/ amperage it should use. 


How do I sort out this information? 
Cheers and thank you. 

Hi Frank-Most of the dynamo flashlights have a "supercapacitor", otherwise known as an "electric double layer" capacitor in them.  The capacitor acts much like a battery in that the dynamo (usually a small brush-type permanent magnet motor) places a charge in the capacitor so the light will still work after you stop turning the dynamo.  Try charging it up really well using the dynamo, and then measure the voltage across the capacitor while the light is shining brightly. this will give you an idea of the voltage you need.  If you're just going to use the mains adapter to charge it and not to actually operate the light, then only a very low current is necessary.-Rick