Theoretically many already have built up supplies I have a house filled with USB-A power adapters and even some USB-C power adapters.
About Apple USB power adapters - Apple Support
As part of our efforts to reach our environmental goals, iPhone models no longer include a power adapter in the box. iPhone continues to work with existing power adapters and USB-A to Lightning cables, such as those included in prior models. iPhone models now include in the box a newer USB‑C to Lightning cable that supports fast charging and is compatible with USB‑C power adapters and computer ports that you might already have. You can use either a USB-A to Lightning cable or the newer USB-C to Lightning cable with your iPhone.
It's perfectly fine to charge with whatever you have, including older USB-A power adapters with USB-A to Lightning cables. My family members are doing that. It's a little bit slower, although some think it might even be beneficial for the life of the battery since it will likely produce less heat when charging. The only caveat is using quality power supplies such as what Apple produces. But aftermarket can be fine too such as from Belkin or Anker. I wouldn't hesitate to use power adapters with the Amazon or Samsung brands. Apple doesn't actually make any and it's not even like their contract manufacturing system where a factory builds something that's completely Apple's design. They have them made by companies such as Flextronics, Salcomp, Artesyn, Foxlink, Lite-ON, etc. They're always identified with the actual manufacturer, which will use its own circuit design, but will build power adapters to Apple's industrial design and meet Apple's specifications.
