"Power head" can be used to actually pump water through plumbing. Such as when it is used to "Power" an under gravel filter system. As such the inlet and outlet are usually reduced to a pipe that can be attached or fitted somehow to the under gravel system up tubes. They are easily adapted to a sponge filter, too, so can be said to "Power" that method of filtration. Some can be run in reverse, but that is a whole other subject. Often the outlet has an attachment where air can be dragged through the system and added to the tank water. Waste of energy IMO. Look up Venturi.
A fountain pump can also be called a power head. The intake is usually diffuse, but the outlet is more pipe-like, and often threaded to accept plumbing fittings. These are not adaptable to UGF, but they can be wrapped externally with a sponge, and often there is a small sponge inside the unit. Clean it often, it is a small sponge.
The Koralia style is not really a power head in that sense. The inlet and outlet are diffuse, and not adaptable to pipe of any sort. They really are pretty much pure circulation pumps, not power heads.
Here are a few more points:
The open inlet and outlet of the Koralia style can allow livestock to get into the works. There is a mesh or grid around it, but the openings are large. Fish have been known to stick their noses in there and get them chewed up. It is possible to fit a sponge over about half of the unit to prevent this. Try the Matala mat for this, or the coarsest of sponge. Perhaps a pond supply item. Coarser than the Aquaclear sponges. It will not look pretty. For more info about this, have a look into the thread that talks about the Hamburg Mattenfilter. You could also put a mesh over it, about as coarse as a hair net or even finer like a window screen. These softer materials will conform to the shape of the Koralia, and can be found in black so they are very subtle. Just be sure it is not really hair net, these are so soft they get sucked into the works. When you cover it like this more debris tends to build up, so it will need cleaning. Not much of a problem, just something to be aware of.
The fountain pump would be similarly awkward. Difficult to cover in a sponge, unless the whole thing is in a box, as is often done in a fountain or pond. While I have a fountain pump in one tank, I usually use them for draining or filling, or otherwise moving water around from one container to another. In that one tank (a riparium set up) it is powering a water fall. They work for circulation, especially for preparing the water for water changes. Great way to dissolve minerals like GH booster. In an aquarium, however, the intake would normally sit on the substrate, or the intake is low on the sides of the pump. This is not great. Plugs up very quickly.
A power head, with its smaller inlet is more adaptable to being covered with a sponge to reduce the chance of livestock injury. The force of water coming out of the outlet is so focused and strong that not many animals are going to get into trouble there. I use Aquaclear sponges or a bit coarser over the intake. While not pretty, the angle of the intake (water enters from the bottom of the unit) allows the sponge to hide behind the plants.
I have used several brands of various pumps.
Suckers: I have not found any that really work well and hold up over time. The closest is the Aquaclear when run over the up tube of the UGF. The uptube is really taking the weight of the pump, and the suction cups are just stabilizing it. Suction cups are replaceable, and quite cheap. Aquaclear also comes with a 'hang on rim' bracket. That is fine, and is adjustable. It will keep the power head near the top, it does not adjust down lower in the tank. These almost never break. Gotta have an empty stretch of rim to hang it on, though. Does not work if you want it hanging on the side and have a typical cover on the tank like a Versa-Top.
Magnets: Koralia. These have held up long and honorably, and I like them so far. But the writing is on the wall, I can feel they are losing it.
Fountain pumps do not usually come with suction cups, but the one I have in that riparium has them. They are toast and never were much good. It might be one of the little junk things from Harbor Freight. Does not matter. Those tiny suction cups are no good, on anything that has them. (Thermometer, heater, filter tubing). Larger suction cups seem to hold up a bit better, and at least are replaceable.
Koralia and similar items are the most easily adjusted to spraying at different angles. Up, down, left, right...
Aquaclear are fine to adjust left and right but are extremely limited up and down.
Fountain pumps can be propped in almost any angle, but will not hold that angle. The larger ones (you do not want a large one here) often come with legs that are somewhat adjustable. (Adjustable meaning: It works with them, or without them!). Some fountain pumps come with a right angled fitting so you can aim the outlet to some extent.
If you add some tubing to the outlet you can lead that tubing where you want (that is how to make a water fall), but then you would have the problem of holding the tubing where you want it and at the angle you want. Could do it with rigid pipe, PVC. I just do not bother going there.