DALI operates at a supply voltage of 16V, current limited at 250mA.
Since the specified voltage range for a 1 bit is between 9.5V and 22.5V, the supply voltage can also be in this range (with 16V being right in the middle of this range. But even if you technically can use a 12V supply, this might not work for setups with longer cable lengths and/or setups with many DALI devices connected. If you have a 12V or 5V power supply, I recommend to use a boost converter to generate 16V.
Note that you always need to current-limit the DALI supply. Just connecting a power supply to the DALI line could destroy your equipment.