The datacenter we were in had dual-sourced grid power (two separate grid connections on opposite sides of the block, coming from different substations) along with a room of batteries (good for iirc 1hr total runtime for the whole datacenter, setup in quad banks, two on each "rail"), _and_ multiple independent massive diesel generators, which they ran and switched power to every month for at least an hour.

And to top it off each rack had its own smaller UPS at the bottom and top, fed off both rails, and each server was fed from both.

We never had a power issue there; in fact SDGE would ask them to throw to the generators during potential brown-out conditions.

Of course this was a datacenter that was a former General Atomics setup iirc ...