Precautionary blackout.
What’s your best guess as to what would make the engineers knock off all the power except for emergency power?
I’m thinking that they had to get into a lockdown space. One ship I managed had 3 levels to get into the transformer room. They had to lock down the engines to get a key to lock down the board to get the key to the transformer space.

https://www.2gb.com/absolutely-horrific ... ed-at-sea/

I have sailed in a few cruise ships but I don't know this one. I would guess she is approx. 50MW 6.6kV diesel-electric. I do not have experience of deliberately blacking out. The only thing I can think of is a problem with the main switchboard, perhaps a generator ACB failed or any ACB on the main bus bars (I have experienced a harmonic filter ACB failure but that caused a blackout), however, the MSWB can be split with the tie-breaker and power could be maintained on the other side. I'm not a leccy but I wouldn't feel comfortable working on half a switchboard where on the other side of the racked out and earthed tie-breaker ACB is a live 6.6 kV bus bar. This is a quick fix though; identify which side is affected, make sure whatever it is, is disconnected or if it cannot be disconnected, split the board and supply the good side and you would have power and still have some propulsion on half motors. I can't think of anything mechanical, for propulsion yes but not a blackout. We are probably all thinking the same thing; the blackout wasn't deliberate. Changing over fuel for arrival Adelaide by any chance?