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Resistors to set what power is available from host is standard on USB2.0, nothing to do with Apple. The host PC/Laptop (or phone / Tablet USB2Go in Host mode) doesn't know or care what the current is used for, it may or may not be used for "charging". A charger basically looks like a Host mode but with no data.
There is a problem with USB2Go, the system that allows EITHER a host (or charger) OR a peripheral (current consumer, can be a light or HDD or USB memory stick or radio receiver, keyboard, camera etc). The problem is that very few tablets or phones can allow a peripheral AND charging on the same port (it needs a special cable too).
Anyway, even if eInk Readers actually have a USB2Go port, it's programmed to be only a slave. Thus a peripheral is ignored. Only a charger or PC/laptop (or phone/Tablet USB2Go port in HOST mode) will work.
Not all USB peripherals (which is what all eInk Readers I've seen are) actually sense the current setting resistors. They generally don't bother if only 100mA or less.
Apple was first to "Break" USB 2.0 spec by having an optical drive that took more than 500mA, so many newer chargers and hosts can supply 1A. Previously things like early 3G modems, DVD writers and early 4G modems used a Y USB cable, were one connector was data and power (500mA) and the second an additional 500mA.
Apple also adds circuitry so Apple devices "know" a PSU or cable etc is Apple approved. This is not part of USB spec.
USB is insecure. So potentially a rogue charger can use the host data pins too and infect a tablet / phone etc. If the Apple charger has suitable circuit on the two data pins, then most non-apple devices will think a laptop/PC is connected.
Also the host is insecure, so a mouse or keyboard (or a memory stick) can use HID driver to infect a tablet/phone with USB2Go, or a laptop/PC. Disabling USB storage autorun or having AV is no protection from HID based attack. Don't "check out" the nice USB stick you found in car park beside your car.
I find my Sony Ericsson charger is fine for everything, though the iPhone4s complains one of the cables is an "unrecognised" device (charges anyway). The Amazon Kindle charger ordered did have a CE mark and is rated 240V, but I don't use it as
1) I think a USA 2 blade connector is illegal and unsafe on 230V
2) Massive radio interference. A similar shape of Tesco bought charger with UK 3 pin plug was also unusable due to radio interference.
There is almost no IN market after approvals testing in USA or Europe now.
Only use genuine Apple stuff with Apple stuff, but Apple is overpriced anyway, by x2.
Do not buy a charger online, but from a local shop. Most fires and Radio Interference are chargers/SMPSUs now, so if it messes AM radio OR gets hot take it back. In Europe, you are 100% entitled to refund if the design is not fit for purpose, for TWO years. If it burns your house down, the retailer is liable for six years.
Manufacturer's warranty is irrelevant in EU and many related (customs union etc) countries. It's two years RETAILER, even if that was the maker via online.
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