On those salvaged flash units, there are two types, most were (?are?) small xenon strobe tubes, probably have a life of no more then a few hundred flashes, the other uses white LEDs.
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The ones with the xenon strobe will have a ~300uF 300~400V capacitor that will light you up but good.
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Been there, done that and still feel the zap. I mean be careful with those tube ends and capacitors! They have enough energy to stop your heart. Use the "keep one hand in your pocket" technique.
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Look up "xenon strobe circuit diagram" on Google for examples of how they are constructed.
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Unless you need a really bright light that lasts a 1/1000 of a second, I'd be really tempted to send them to the electronic recycler.