hello friend
i read your current problem
if a charger have 500 ma amp u just know its coreect or take a load test u put connet the variable resistor and change load linearly and take the voltage reading and current readinf ok u increase load untill volatge will down thats point ur is current rating of the charger or power source in these case ur charger will be ok u just connet a500ma load and check the volage he didnt down tha reted volatge