As long as both ends of your U tube are below water then it will continue its siphon once the electricity is back on.
There are some benefits with some designs over other designs. For instance compare these two:
Lifereef Filter Systems Economy Prefilter Boxes, 6 gpm
If I had to pick from the two above I'd definitely go for the 'Life Reef' overflow. Primarily because the outer compartment is quite longer than most other siphon overflows. When it comes to creating a strong and fast siphon … the farther the drop … a stronger/faster siphon will be the result. This is why the Life Reef models are rated for higher volume even though they are of similar dimensions to lower
gph rated overflows.
Also you'll notice that the Life Reef overflows have a baffle in their outer compartments and their stand pipe is set low. This baffle keeps the U tube below water at all times (even during power outages) and since the standpipe is set lower than the baffle it ensures top performance with its siphon action. With some study of the design you’ll see what I’m talking about.
Before actually making one yourself you might consider purchasing one. My 1st overflow was the Equatic Eco one and I’m VERY glad that I didn’t fiddle with making one myself.
Also the very best type of overflow is an internal overflow (not a siphon). Even 1 corner overflow is much more reliable than any siphon overflow. For the price of a couple pieces of glass, a cheap diamond hole saw, and a tube of silicone … you could have one of the best overflows possible and at a lower cost.
