As reported by several users and a post at the Apple Core by Jason O'Grady, some iPhone AC adapters are apparently suddenly failing to deliver a charge, forcing users to connect their iPhones via USB to their computers in order to properly charge.
"Both me and my wifeâ??s iPhone AC adapters died within 24 hours of each other. I notice mine was having trouble yesterday when I grabbed my iPhone in the morning only to notice that it hadn't charged overnight. Last night I grabbed my wifeâ??s adapter and it was dead too."
If you are experiencing a similar issue, you may want to first try resetting your iPhone by pressing and hold the Sleep/Wake button (on the top right of the unit) and the Home button (circular button on the iPhone's face) simultaneously for at least 10 seconds, until the Apple logo appears. After doing so, reconnect it to AC power and check for a charge.
UPDATE: We've now received reports that removing the pronged portion of the iPhone AC adapter (sometimes called the "duck") and reconnecting it, ensuring there is a snug fit, resolves problems with power delivery.
iPhone Atlas reader Kevin McCormick writes:
"Removing and replacing the pronged portion of the power adapter can solve the problem of the units losing contact. Sometimes the pronged portion needs to removed and replaced several times for the proper contact to take place."
Failing the above, you may want to contact Apple for replacement.