I have a recipe for Thai Green Curry that calls for evaporated milk, which I don't have. I do have sweetened condensed milk, will that do?
Sweetened condensed milk has a 40% sugar content. It is very sweet, suitable for desserts and such. It is entirely too sweet to substituted into a curry.
The consistency is drastically different. Evaporated milk is about the same consistency as heavy cream. Sweetened condensed milk, because of its high sugar content, is more the consistency of a warm caramel.
Also, they are different colors, evaporated milk is white, sweetened condensed is light brown.
They are nearly identical, if you don't count the sweetened bit, it's around 40% sugar, while evaporated milk is just milk with around 60% of the water removed. You might be able to substitute it in that particular recipe, if you were planning on making it sweet, and use a bit less than the recipe calls for.
(not directly answering the question).
As others have said, it's not a good substitution.
If you had asked what I would replace it with, I'd personally use coconut milk, because that's what I have in my pantry, and I like how it works in curries.
A closer substitution would be half-and-half or light cream, but they would just have a closer fat ratio as evaporated milk, they wouldn't have the sugar and such concentrated as well.
The two are similar, obviously the sugar in sweetened condensed milk is the big difference.
They both start the same way, about 60% of the water is removed from milk by boiling at reduced pressure and temperature. Evaporated milk is then sterilized by heating it which gives it a caramel flavor. Sweetened condensed milk isn't sterilized the same way, instead sugar is added and that keeps bacteria from growing in it. (There are other steps for both that I've left out, see Wikipedia and this book excerpt.
It's going to be really, really sweet. If you don't like that, then no, you can't.
If, however, you have my vicious sweet tooth, it can be a neat variant. I personally love to switch condensed milk for evaporated in a potato soup and add ham. The final soup is sweet enough to be a dessert, but still quite tasty.
....I now want to try it in a curry, actually.