12v USB A to C Cables - Help please

There are a lot of phone chargers out there that charge at 12V. (eg. Xiaomi has 12v 2.25A = 27W, Samsung has 12v 2.1A = 25W etc.) that are NOT usb c PD, but use usb A to usb C.
However I can't find any usb A to usb C cables that allow 12V. The most I see if 5V.
Am I missing something?? Basically none of these chargers could actually provide the stated Wattage given the usb cable limitations.

Background context:
I've got a Xiaomi Mi 9 with 27W charger, but using AccuBattery & Ampere, noticed it only ever charged at 15W (roughly 5V x 3A).
My wife has the new Samsung Galaxy S21 and so I bought one of these Samsung 25W chargers as they were cheaper than the equivalent 25W PD chargers:
https://www.dicksmith.com.au/da/buy/samsung-usb-fast-chargin...
I noticed the same thing, that it only draws 15W.
So I thought it must be the usb cables. Note: I'm using Baseus fast charge Usb A to usb C cables.
Looking online I noticed I can't find any usb A to usb C cable that allows 12V. Hence my dilemma.

Other than throwing all these chargers & cables in the bin and starting over with USB PD chargers & cables, what should I do?

Thanks

Comments

  • Within the USB specification (USB-C, USB-PD), there is no such thing as a "12 V A-to-C cable".

    What's actually happening is the 9V/12V level on these chargers probably uses the proprietary QC2.0/QC3.0 protocols (which Samsung has rebranded AFC). This should work with your normal A-to-C cable.

    Keep in mind that:

    • QC will almost never reach the peak rated power. If it ever does, it's likely only when the battery is near empty.
    • Software tools such as Ampere are often not entirely accurate. You really need an inline meter (one that supports QC/9-12V) to measure the power flowing over the wire.
    • With QC, most often you'll end up at 9V even if the charger and device both support 12V.
    • It's very likely that your "15 W" is actually ~1.6 A @ 9 V rather than 3 A @ 5 V.
    • IME Samsung phones will actually reduce power draw and charge rate while the screen is on. Most likely to prevent overheating. i.e it'll charge faster if you aren't actively staring with Ampere etc.
  • Google is your friend. Have a read of the following to see if your device meets the spec for fast/optimal charging:
    https://www.samsung.com/us/mobile/mobile-accessories/phones/...

    To read up on what fast charging is:
    https://au.pcmag.com/phone/52811/what-is-fast-charging