Question Phone stops charging when computer is shut down

[ultrarunner100]

Hey all;
I've got a new build with Asus Tuf Gaming X570 WiFi, Ryzen 7 3700X.
The PSU is Seasonic Focus GM-750.

Last night, I had my phone (Moto G7 Optimo) (turned off) plugged into a USB port using a standard USB A to C cable, which also transmits data.
I shut the computer down (not sleep).
The phone was at 58% charge when I left it.
This morning, the phone was still at 58% charge.
This was odd, as I had charged the phone using the same USB port and cable while the computer was shut down before.

So I did some experimenting, and discovered the following:

1. If the computer is shut down while the phone is charging (phone on or off) through a standard USB cable, the phone will stop charging.
2. If the phone is then disconnected, then reconnected to the USB port (computer still off), it will start charging at the slow (0.5A) rate.
3. If the phone is plugged into the USB port with power only - no data connection - it does not stop charging when the computer is shut down, and charges at a faster (1A) rate.

I have a USB dongle that measures voltage and current, and has two ports; one is power and data, while the other is power only - for fast charge.
I think I now understand how certain USB cables are sold as fast charge but no data, and others are standard USB cables. I also find some cables that claim to allow fast charging and transmit data. I guess with some phones this is possible, but it appears that when my phone is connected to a USB port on my PC using a standard cable (with data), it will only charge at the slow rate.

I actually prefer the slower rate, as it is better for the battery. However, I need to remember to plug the phone into the USB for charging after the PC has been shut down, or just leave the PC running.

 

[Ralston18]

Neither the PSU nor the motherboard is a "battery". Something else is going on and that something is not good.

Does "charging" as described in #2 above continue if the PSU is unplugged from the wall outlet?

Do you have any independently powered USB hubs connected to your computer?

Any UPS's, surge protectors,and so forth?

What USB dongle are you using to measure voltage and current?

The reason I am asking questions is that if I am working on a computer with power off and/or unplugged there should be no power anywhere; USB or ports or otherwise.

Hopefully I am making some error of omission or commission regarding your post.

Need to understand the bigger picture.....

 

[ultrarunner100]

I'm sorry. I should have been more clear about what I meant by the computer being 'shut down'. The power switch on the PSU is ON. There are lights on the MOBO.
The computer is only shut down so far as Windows or other OS goes, but there is still power on the MOBO.
There is a feature that allows USB power to remain on when the computer has been 'shut down' through the OS.
I understand that when the computer is in 'sleep' mode, everything would remain powered, but this system was designed to allow charging of devices from its USB ports even when the computer is shut down by the OS.

I would need to go into the <BIOS> setup to see what choices I have for USB power, but I would want the USB to remain powered at all times.

The dongle I am using is a generic device that plugs into a USB port and has the voltage and current displays, and two USB A ports. One port carries data along with power, while the other carries only power.
I believe this is done for exactly the purpose I have discovered; to allow any phone to fast-charge when the system is off (no data on the port).
I am sure that different phones will handle the situation I have described in different ways.