Hi Femi,
I quoted a Q&A because its quite relevant to your question:
Question:
What happens if I plug a device that uses a 1A USB charger into a 2A USB socket? Or a 0.5A USB socket?
Answer:
So, there's a slight difference when talking about devices vs. chargers.
A 1A device means that, for a power supply at a certain voltage (5V for USB), the device will "ask" for 1A from the power supply.
For a 1A charger, it means the electronic devices in the charger can handle 1A before they break. However, the charger will only supply as much current as the device it's powering is asking for.
So, plugging a 1A device into a 2A charger will be fine. The device will only ask for 1A, and the charger is designed to supply up to 2A. No problem!
However, plugging a 1A device into a 0.5A charger may cause a problem. The device will ask for 1A, but the charger can only supply 0.5A. What happens depends on how the charger is designed. In some chargers, it could unrepairably damage the charger. You might hear something pop, smell some burning metal, or see some smoke. If it was a really cheap charger, that's probably what will happen. In better chargers, there will likely be a fuse or other current limiting device to cut off the power before the charger is damaged. Your device won't get any power, but the charger either won't be harmed or is much easier to fix.
It all boils down to the concept of V=IR. (Voltage = Current x Resistance). Voltage is essentially constant. A charger will convert the 120V AC from a wall outlet to a constant 5V DC to give the USB device, or a car charger will convert the 12V DC voltage to a 5V DC voltage. More on that in a sec. So voltage is constant. Resistance is determined by the device - it's a property of the circuitry that the device contains. So resistance is also constant. Essentially, resistance determines how much current the device will ask for at a certain voltage. Look at the equation again. With a constant voltage and a constant resistance, you can always solve for a current. A 1A device has a resistance such that it will draw 1A from a 5V DC power source. If the power source is rated at 1A or higher - you're all set. If the power source is rated at less than 1A, you might have a problem.
And to answer your final question: No, it won't matter if the charger is AC or DC. If the charger is designed to output 1A at 5V, all components in the charger will be designed to make sure they can handle that amount of power all the way from the power source (120V AC from a US wall outlet or 12V DC from your car's cigarette lighter) to the charger output.
http://goo.gl/mUr17xHope it helps,
