SNOOZ White Noise Machine uses a Type A (U.S. plug) so a plug adapter would be needed, but no voltage converter is needed as SNOOZ's power adapter is internationally compatible (100-240V).
SNOOZ Go charges through a standard USB cable which should work without issue internationally.
SNOOZ Button uses a USB-C power connector so a plug adapter may be needed, but no voltage converter is needed as Button's power adapter is internationally compatible (100-240V).