many USB ports (either 1.1 or 2.0) fail to provide the 5V required by the spec. So you are likely right about the issue. One way around it is to buy a powered USB hub that states if provides the proper 5V via the ports. Not ideal but it does work. I am lucky my laptops all pass that spec. My main lappy has four USB ports all of which are in active mode and provide a very steady 5V.
Somewhere I once ran across a voltage tester for USB ports but I never saved the link. You might be able to find one somewhere. It should be under $10 and is a nice tool to have if weird things happen with yur USB device. It could be an early warning sign of a failing motherboard in need of replacement or repair.
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