IPAD 2 Won't Charge on USB port on my laptop, my desktop Mac but will charge via the wall plug

Question

I am confused on what to do with my IPAD 2.  It won't charge via my USB Port on my PC that I travel with.  Also I just purchased a new desktop Mac and it will not charge on that USB port either.  But it will charge via the Wall Plug that came with it.  I am worried when I travel to different countries to use the wall plug.  I have an adapter to switch power.  I am from Canada and travel oversees where the power is 240 vs the 120 at home.  If I use my plug adapter and plug in my ipad to the wall Will I destroy the battey in my IPAD 2.  I love my ipad to travel with but it is very frustrating when it will not charge on my PC or on the airplane.  Then I am afraid to use the wall plug in the airport because of the difference in power.  Would really appreciate some help here because I am oversees 2 weeks a month and only get a couple days use of my IPAD.  I have all my books and everything on it and need to be able to recharge it.  Does anyone have any suggestions?
Thanks
Confused!!!!

Answer 1

For better future reference, you should be aware that the voltage means nothing when it comes to charging power. All that that is telling you is that the Power Adapter will work across that voltage range, i.e., you don't need a transformer to plug it into the outlet (although you may need different plugs, which is a separate topic).
What matters is the amperage (A) and the power in watts (W). The Power Adapter puts out 2 A @ 5 VDC (volts DC), which means it's producing 10 watts of power. It will output that across the entire voltage range.
A high-power USB port on a PC will put out 0.5A @ 5VDC, or 2.5 W. Be aware that not all of the ports on any given PC are likely to be putting out even that much power, at may well be putting out less than half as much. That's why you'll often see the "Not Charging" when plugged into a USB port, especially on Windoze laptops, and why it will charge very slowly even when it works.
FYI, the charger which is sold with the iPhone looks identical, is called the same thing, but only puts out 1A. It will work on the iPad but will charge more slowly. By that same token, the iPad charger will charge an iPhone just fine, it will just charge faster.