I have three mobile phone chargers with rating 5V 500mAh, 5V 1Ah , 5V 2Ah. When I charge my phone Mi 4i with these chargers , the charging time is different. It means all these chargers drive different current through my phone's charging circuit. 

So my question is, how can same voltage sources(5V) drive different current ( here 500mA , 1A and 2A) through same load(my phone)??