Unable to charge the speaker system when using a commercial USB AC adaptor.

Check the following:

• If you use an AC adaptor other than the one supplied with the speaker, it must be a 15 W (or higher) USB Power Delivery (USB PD) compatible AC adaptor and use a USB Type-C cable (compliant with the USB standard) that supports USB PD.
  Note: If you are not sure if the AC adaptor or USB Type-C cable supports USB PD, consult the adaptor or cable manufacturer.
• If you charge the speaker while you are using it, it may take a longer period of time to complete the charge. We recommend turning off the speaker while charging.
• Depending on the specifications of the USB AC adaptor, when you use the speaker with high volume, the remaining battery may decrease or the speaker may turn off even though the adaptor is connected to the AC outlet (mains). This is not a malfunction. If this occurs, turn off the speaker, wait until the speaker is fully charged, and then start using it again.