How do I know if the Noise Scout Watch is charging correctly or not?

• Connect the charging cradle to a power adapter, and plug in the power adapter.
• Plug your watch with the charging cradle. Align and attach the charging contacts of your watch to those of the charging cradle until you can see the battery charging display on the watch face.
• When your watch is fully charged, 100% will be displayed on the watch screen and the charging will stop automatically. If the battery level is below 100% keep the charger connected until it completes charging.

What power supply should I use?