Cell phone chargers are they all the same?

Is there a difference in the mini USB chargers for cell phones? Went on a long car trip, and phone would not charge. Figured bad battery. Went to a cell phone store, bought new charger. Seemed a little loose. Got home, plugged it in and bada bing, charged like a champ. In the meantime, bought a charger and a battery, to no avail. So now I am just curious.