While it can’t hurt to try, I doubt you’ll easily get the standard delay money from a flight directly affected by ATL power outage issues: this is exactly the sort of widespread facility or infrastructure issue the regulation intended to exempt with “extraordinary circumstances”. IIRC, the detailed language is something like “under the airline’s actual control”. Data center outage? Absolutely. Airport authority outage? That’s a much, much tougher case to make.

For a cascade delay, like AMS-SLC, you might be able to argue that the flight shouldn’t have been operationally affected by an unrelated incident thousands of kilometers away from both your origin and destination. Delta will probably deny you, but the Dutch regulatory body might take a bit more kindly to the argument.

Where you have a slam dunk case is if they failed in any of the “duty of care” obligations - food, prompt rebooking, hotel, a free phone call, etc...

Good luck! EC compensation is possible to get, but steel yourself for a very, very long fight... It’s worth asking anyway though because you’re almost guaranteed to get some number of SlyMiles when they initially decline your claim, which may or may not be enough to make you happy...