I am having an issue with my S9 - while its installing an update the phone just restarts and continues (by this I mean it shows the Samsung Galaxy S9 Powered By Android screen then it goes black and this process repeats until the battery is at 0%). This is the second time this has happened - the last time this happened we sent it to get repaired and its been working until today. I have tried the Volume Down + Power Button method and that did not work, I also tried holding Volume Up + Bixby + Power and that displayed the 'Installing system update' page and installed the update from 28% to 35%, where it then came up with an 'Error' and the reboot loop continued.
@jveeren: Sorry to hear you're having issues updating your Galaxy S9. If you're unable to complete the update via WiFi then please download Smart Switch for PC or Mac using the link below, connect your phone using your USB cable and look for an Update prompt on the home screen. https://www.samsung.com/us/support/owners/app/smart-switch
Are you able to complete the update via this channel?