At first glance, the iXP1-500 seems like a tidy solution. For only US$5, you get a tiny doohicky that acts as a bridge between the iPad and the under-powered computer. Once connected, it will eliminate the "Not charging" message and power up your iPad. So what's the problem?
First of all, their website isn't entirely correct in saying that "users of non Apple computer and some Apple computers cannot charge the iPad unless they use an electrical wallplate," as we've demonstrated. Additionally, NASA Electrical I&T Engineer Frederick Maxwell notes on the Cult of Mac blog: "The battery in an iPad is a dual-cell, parallel-wired, Lithium-Polymer that weighs a whopping 148 grams (5.5ozs) and provides 24.8 watt-hours of capacity. The dongle in the article has a total weight of 0.1 ounce, including connector, casing, and all internal parts. It can't work. Period."
As John Brownlee notes at CoM, this thing is probably tricking the iPad into believing it's receiving 10w of power, there by eliminating the "Not charging" message. Eliminating the message could convince some shoppers that their $15 ($5 for the dongle + shipping) was well spent. But it's just a workaround, and you didn't need to spend the $15 in the first place.
The moral of the story is twofold. First, buyer beware. Secondly, you can charge your iPad from an underpowered USB port -- just slowly -- as it is.