From Newsgroup: comp.misc

Got a new Samsung phone with a USB Type-C port. That happily connects to
both my main workstation and my laptop, and will accept charging from
both. I tried a Type-A-to-Type-C cable for the former, and a Type-C-to-
Type-C cable on both, and everything worked fine. I have also successfully done data transfers on the workstation -- didn’t actually try the laptop yet, but I imagine that will work too.

I have this old power adapter brick (says it’s “Asus” brand) with a USB Type-A port on its back. I was able to use that to charge my old phone
with a Micro-USB connector (yeah, that old) and suitable cable, but the
new phone will not accept any power from it via a Type-A-to-Type-C cable.

As far as I know, that adapter is completely dumb, knows nothing of “USB- PD” or any such, so it should just be putting out 5V through the power
pins and that’s it. Says it’s rated for 2A. But the new phone doesn’t want
to look at that.

Any thoughts on what might be going wrong? Not enough current, perhaps?

Thanks for any suggestions.
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From Newsgroup: comp.misc

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:

As far as I know, that adapter is completely dumb, knows nothing of "USB-
PD" or any such, so it should just be putting out 5V through the power
pins and that's it. Says it's rated for 2A. But the new phone doesn't want to look at that.

Any thoughts on what might be going wrong? Not enough current, perhaps?

Surely you've answered your own question. The phone wants to chat
with the charger and it's not talking, so it's not happy.
Officially USB devices were supposed to negotiate with the host
and get permission before using >100mA. Since nobody paid
attention to that, dumb chargers ended up working anyway. I guess
the new USB-PD programmers are taking the standards more seriously.

The higher-rated dumb chargers (such as your 2A one) might also put
a resistor between the data lines to indicate that devices can pull
more current than the USB spec allows. Again it's up to the phone
designers whether they include the ability to check for that. You'd
hope they'd try to be backwards-compatible, but apparantly not.
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From Newsgroup: comp.misc

On 18/10/2025 04:38, Lawrence D’Oliveiro wrote:

Any thoughts on what might be going wrong? Not enough current, perhaps?

In my case I have a USB2 port on my phone but it uses a USB-C connector.
I have USB3 A<>C and USB2 A<>C cables and the phone charges with
anything and everything.

Some USB A ports on PCs etc. can only provide 500mA. Some can provide 2A
or more. There's normally symbols to show the port is high current and
on laptops, also tell you the port can be used to charge something when
the laptop is switched off.

If your new phone has USB3 it may well be more correctly implementing
the CC pin feature on the C connector. The C connector end of the cables
has a resistor connecting CC to VBUS (+5V) and is used to signal things including the charging current available.

It's possible your A<>C cable is saying that high current charging is available. When used with your main PC if you plug this cable into an A
port which is higher current cable, the phone is told high current and
starts drawing higher current and the PC provides the current and
everyone is happy.

However, on your old 2A charger, the phone may be trying to draw over 2A
and the charge will be a switched mode which sees more than 2A load and switches off as it sees above 2A as a fault.

The probable fix is to buy an A<>C cable with a known value resistor
inside which suggests buying something more upmarket than an AliExpress bargain!

It all used to be simple with USB... emerging new standards and often
sub-par components result in stuff not working any more when it should.

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