After a quick check with the multimeter on my Magicshine battery pack, the centre pin is positive, the outside is negative. If your light takes a 7.4 V Li-ion battery pack (most of the Chinese lights do) it should be the same - I've got a battery pack that came from one of those cheap lights (which lasted all of one hour!) which will run my Magicshine quite happily.
If your power supply's a bench power supply, with adjustable voltage, I'd wind the output down to zero before connecting it and then increase the voltage slowly whilst checking that the current doesn't rise too fast: anything more than 1-2 Amps is probably too much.
