This issue has been documented all over the internet and on this forum for many years.
If one connects a device to the aux in on the speaker it generates a 50Hz hum. This hum can only be stopped by disconnecting the power supply. I use this speaker as a PC monitor so this is not practical. Most other 4.5 to 5 V DC power supplies are only 500ma (as against 1000ma (1A)) and therefore cannot charge the speaker. (and yes, i tried a new cable).
One would think that a prestigious company like Bose would have sorted this issue out years ago, I have had many Bose products in the past and was looking at Bose sound bars and outside speakers. This issue has made me re-think this choice..