a question about USB via computer charging and usb power outlet charging, are they the same? sometimes i find the power charging outlet to be more faster

on the side note, my device was fully charged 10 hrs ago, i turned off the device and left it, now its been 8 mins and i have put it on charge via computer and the battry is not full

edit: it took about 30 mins for the light to become green again :s...