The total 'techie' answer is to double check the mAh output of the charger (should be 800-1000).
But the layman's answer is if the Samsung charger is for a smartphone, it should charge your Droid Razr just fine.
Oh, p.s., sorry to contradict a fellow staff member, but I wouldn't put much faith in cheap aftermarket chargers from eBay unless you know what you're doing; and even then . . . .
good luck