Hi - the expression refers to an unexpected outcome. e.g. I was overtaken by surprise when the rain stopped and the sun shone through. Or I was overtaken by surprise when I suddenly saw my best friend standing next to me at the station.

For me, 'overcome' is the normal thing to say. I've never heard 'overtaken by surprise'

I think what you want to say is "taken by surprise." "Taken by surprise" is just another way to say that someone or something is surprised. Example: We were taken by surprise when the bird suddenly flew out of the birdhouse.

Overtaken probably not the best choice - taken by surprise is a better expression - e.g I was taken by surprise when I saw my friend unexpectedly at the bus stop.