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

Check the following:

• If using a commercial USB AC adaptor and not 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 (Power Delivery), consult the adaptor or cable manufacturer.
• If you charge the speaker while using it, it may take longer to complete the charge. We recommend turning off the speaker while charging.
• Depending on the specifications of the USB AC adaptor, when you use a speaker at a high volume, the remaining battery may decrease, or the speaker system may turn off even while the speaker system is connected to an AC outlet by the USB AC adaptor. This is not a malfunction. If this occurs, turn off the speaker system and let the battery fully charge itself before you use the speaker system again.