different types of filters in theory will be better in a power outage. The more volume of water the filter itself holds the better, more food and oxygen available then to the bacteria when flow stops. In most filters once the power is lost and flow stops food will quickly be depleted. It usually doesn't matter unless its a long power outage. bacteria should go a day without much die off. A internal filter though, like a sponge filter would be best since it is actually in the tank with very little separating the media from the entire tank volume. Even with no flow diffusion of wastes and water movement from the fish and heater are on your side even if it is minimal. A canister has a large water volume so often will hold out longer then say a HOB with a very small water volume. The HOB will need your attention first, but its easy enough to manually scoop water from the tank and pour it into the HOB but small volume and the design doesn't make it as effective. Some HOBs have bio-wheels on them which are the first media that needs attention in a power outage. Since this is exposed media it is at great risk of drying out and should be just dropped in the tank so it is floating or sunk as soon as power is lost. It can be put back as soon as power returns. Canisters I usually service if it has been 12 hours with no power, these are harder then a HOB but more efficient. If you disconnect the (return)hose from the spray bar and drop it below water level to a bucket you have an instant siphon that pulls water from the tank through the filter to a bucket. In a minuet or so I can pull 3 gallons through my canister then just pour the bucket back into the tank. I usually pull 10 gallons through on my 55gallon then let it sit again. The main focus is to avoid bacteria from starving. Ammonia build up in tank may be only temporary during a poweroutage, but if your bacteria starves it can lead to a mini cycle. It would be something I would really like to see tested out in an experiment. Its a lot more complicated then it seems on the surface though... other things too like if bagging all the media and throwing it in the fridge would slow down metabolism enough to sustain it longer (or maybe just kill it lol)... biologically the warmer it is the faster it grows, the more it eats, and the sooner it dies.