We’ve been reporting that the next iPhones will come with fast chargers in the box that will bring triple the refill speed of the standard charger provided with current iPhones. The cable will still have a Lightning connector on one end, but will use a USB Type-C, also goes into its port flipped either way, and a larger power block.

With this new adapter bundle comes the challenge of producing enough of them not only to fulfill iPhone shipments, but to get extra for replacements. You’ll want to keep track of where you place your block if you buy a new iPhone this fall, because it’s likely you’ll have to wait until 2019 to get a new block and you’ll end up making do with a slow charging adapter or go crazy with a MacBook charger — which you can already do.

You shouldn’t, however, buy a knock-off charger, even if you tear apart its circuitry and know it’s a safe, sound and USB-compliant device. Macotakara now reports from sources that as Apple plans on making its hardware compliant with the USB Power Delivery Rev. 3.0 standard, you may expect significantly slower speeds.

The pertinent stub of the standard is something called C-AUTH, which checks if a charging implement is USB-compliant in general and whether it is on a white list. Manufacturers of phones, tablets and other tech can tailor this whitelist to their liking. That means that even if you have a fast charger for a non-Apple phone that’s USB Power Delivery-compliant like the Google Pixel 2, it probably won’t be on the whitelist.

In the case of Apple, the company has its roster of partners producing accessories for its Made for iPhone/iPad programs. It should also be pointed out that the California corporation is a major member of the USB Forum that governs standards over universal serial busing and is obligated to deploy standards as determined by the forum.

If the charging block is not on the white list, any data-linked functions will be disallowed and charging rates will be limited to 2.5 watts. For perspective, the standard rate for the current white cubes is 5W and the maximum potential rate is 18W.

Once again, do not lose your charger.