Well look at this. The iPhone 4 takes an average of 23 percent longer to charge while charging via USB than it does while charging via a standard electrical outlet.

Now, of course, this isn’t exactly breaking news in the traditional sense of the phrase—I’d be shocked if you didn’t know, or at least suspect, that it takes longer to charge via USB than via an outlet.

In dollars and cents, that means the iPhone 4 takes an extra 30 minutes to charge via USB.

And there’s this handy chart.

The more you know, folks. The more you know.

[via iClarified]