Bluetooth headsets, like many portable devices can be charged on a USB port on a computer, which supply less than 1A, so either charger would be suitable.
Looking at the manual, a full charge should take two hours, so half an hour seems a little quick.
Perhaps it was part charged?
You could see if you can listen to music for six hours on a charge, and if so how long it takes to charge then.
The manual can be found here.
S9 user guide - Motorola
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