I currently have a device on the market that is powered by a 12V, 500mA wall adapter. At 12V, it draws about 175mA. We have been asked by a very large company if we can supply a USB 1 or 2 computer powered version. I have been experimenting with some cheap Ebay 5V to 12V buck step up converters where the PCB is molded right in a USB cable. Using my power supply, my device normally draws about 400mA, on the USB 5V side of the converter but can momentarily jump to a little over 500mA at certain times. I have tested my setup on 2 laptops and 4 desktop computers and the arrangement is fine. That is, I haven't fried any USB ports yet by exceeding 500mA. I'm a chemical engineer so I'm somewhat lost when it comes to electronics and double E stuff. I don't want the liability of frying thousands of this companies computers so is this safe or should I try another approach?