What could be causing this erratic power/voltage behavior with USB ports on a desktop PC?

Question

In short, I am having issues with what looks like to be power management of USB devices by my computer. I have had the following symptoms pretty much since I bought it in November 2021.

When I connect some USB flash drives, the mouse dongle range drops from few meters to 20cm or so, to the point where I sometimes need to use the mouse on my knee to make it close enough.

• It doesn't matter which USB ports I use — I haven't tested all of them, but a bunch of different combinations and the effect was always the same; be it a dedicated mouse dongle or a Bluetooth dongle.
• I also made sure to have every other USB device disconnected at the time, for the same effect.

I regularly have issues with USB Wi-Fi Adapters:

• The internet suddenly stops working and I need to either turn the wifi off completely or go as far as uninstall the device in Device Manager (Windows) and refresh for the drivers to be reinstalled.
• On occasion I had to change which USB port I used and it seemed to help.
• I am on my 3rd Adapter, two somehow stopped working and had to be thrown out.
• Today the problems went to the point, where I couldn't use the internet at all, reinstalling the device and changing ports didn't help, I switched to a stronger router and relocated it for the dongle to start working.
• But it's still working extremely unreliable, speedtest gives results between 10-200 (Ping) / 0.25-40 (Download) / 10-40 (Upload), while my wife's computer which is right next to mine get consistent ~20ms / 60 / 40. Not a problem with the adapter, since she gets the same results even if we switch devices.

Additional details:

• I've tested a PCI Wifi card and had the same result.
• I also tested with a powered-up USB Hub, the same result.
• I don't think it's USB 3 interference because of the above + I tested on USB 2 ports as well for the same result.
• My Motherboard is Gigabyte B550 GAMING X (which I've since learned is in the "LOL NOPE" tier)
• My PSU is MSI MPG A650GF

All of the above leads me to believe there is something wrong with the power of my machine but I don't even have a clue where to start investigating this issue. Seems unlikely to be caused by weak power supply, I get estimated 430W requirement and have 650W power supply.

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At this point I've replaced the motherboard and all of the problems have gone away. The old one will be sent back on warranty and I'll post my own answer if I get information back what was wrong.

What could be causing this erratic power/voltage behavior with USB ports on a desktop PC?

Answer 1

You need to check the 5v rail. Some motherboard manufacturers give you software that you can use to monitor the voltages. Otherwise, you will need a volt/ohm meter.

Also this device will help you see what is actually happening to the voltages of your USB devices.

https://www.amazon.com/dp/B07FL5Y821/

Many other brands exist, but you will be able to precisely monitor 5v at the USB port level.

Some power supplies in fact offer a ton of watts via 12v rails, but skimp on the 5v rail so more information is needed to diagnose that. Like which exact power supply you have.

Answer 2

This sounds like an power supply problem.

1. Do you have a powered usb hub? Maybe someone can borrow you one, or you have a hub in your screen? Connect all usb devices to that and see if it stabilizes.
2. Get a 5$ multimeter and measure the power supply voltages - 12V & 5V rails can be easily accessed via molex connector and should stay 12 and 5V respectively, with max deviation of 5%. If those stay within specs, measure the usb ports themselves - use a snipped usb cable from old device, plug it in, and check voltage between pairs, it should be 5V between two of them and 0-ish between the rest.

Your power supply wattage is irrelevant, manufacturer and model matters. Please list the psu model to see if its in the 'do-not-buy' list.