I just bought the SonicWare Liven synthesizer and it didn’t come with a power supply.

These units do not include power supplies. Sonicware sells a power supply for the Liven units, or you may also use power supplies for the Korg Volca series, as both have the same voltage, current, and connector size specifications. Here are two supplies that will work:

https://www.perfectcircuit.com/sonicware-9v-power-supply-for-liven-grooveboxes.html

https://www.perfectcircuit.com/korg-volca-9v-power-supply.html