It's been 20 plus years since I worked on ships that came into our local port so treat this info with a grain of salt.
I have worked on, maintained and fault found all of the gear mentioned below
Most large vessels have three main alternators driven by 3 separate diesel engines. Each alternator is somewhere in the vicinity of 600kW and up and run on heavy fuel oil, the same as the main engine.
This fuel at room temperature is a tar like substance and is heated to decrease its viscosity. It is then run through centrifugal separators to get rid of impurities prior to being fed to the engines
Under normal electrical load conditions only one alternator powers the main switchboard.
There are 2 methods of bringing a second or third main alternator on line. Automatically or manually. Both methods are the same just controlled by hand or actuators.
The alternator to be brought on line is started, its governor is adjusted to bring the frequency of the alternators’ output up as close as possible as the one already on line.
At this stage, fine adjustments are made to the speed to get the three phases in sync using either the three old school synchro lights or simply an analogue meter whose 12 o'clock position corresponds to phase alignment.
As the needle or lights come around slowly to the synchronized position it is connected to the main bus.
At this stage, depending on what you want to do the load sharing is adjusted by increasing or decreasing the governors whilst at the same time watching the frequency.
For example if you want to bring an extra alternator online you would start the diesel, synchronize and connect it to the bus. Once connected you increase the governor speed which has the effect of increasing that generators load and decreasing the load on the existing one. If the line frequency starts getting too high then you decrease the speed of the alternator with the most load.
Most of the ships at that time didn’t have autonomous load sharing, we did start to introduce these systems onto some vessels but that’s another story.
Ships that had bow thrusters needed two geny’s on line. Namely to handle the start up current but consequently as a safety measure, should one trip off.
All of the bow thrusters I had seen had variable pitch propellers and had to be at zero pitch before they could be started. Some were DOL others employed old school resistance starters with the latter method having massive inline resistance starters or slipring motors with resistors in their rotor circuits shorted out in stages
They all have an emergency alternator that runs on normal diesel fuel that have a substantially lower kW rating and start automatically when power loss is detected on the main buss. These were also air start.
When the emergency alternator is running only a small subset of essential equipment is powered and the main generators can't be switched onto the main bus until the emergency geny is ofline
In addition to emergency AC there are large banks of single cell batteries stacked up to create an emergency 24VDC supply for navigation, radios etc.
Some vessels had more than one bank for DC supplie for other various systems. One example of this was for a vessel that had three internal gantry cranes used to move and store large 30 tonne slabs of steel with large electro magnets. A large bank of AGM batteries making up 110VDC were used in the event of loss of power to ensure a slab wouldn’t detach.
In the steering flat where the top of the rudder comes into the ship, there would be a series of hydraulic rams actuated by a large pump and indeed had a backup. The port and starboard pumps. In fact there is very little equipment on a ship that doesn’t have 2 of everything.
If that vessel had a bow thruster it would explain why all the deck lights turned on and off as with the emergency geny, only a few would have turned on but the bow thruster certainly could NOT be run off of it so they would have been attempting to put the main genys back online which presumably tripped when attempting to restart the bow thruster.
Having worked on many overseas ships they were often poorly maintained with a lot of safety stuff spragged out. Many times when surveyors were called onboard to inspect dodgy vessels, they would be laid up and barred from going to sea until rudimentary safety gear was repaired.
Speculating here, but if they were attempting to restart the bow thruster any number of issues would certainly cause the generators to trip off
edit: typo bow thruster can not be run from emergency generator