[Plugin: WP Super Cache] How Does Super Cache Impact SEO?

I’m thinking of adding this plugin to one of my blogs but was wondering what it does to the permalink structure.

I have my permalink structure set to display in the format of http://www.mysite.com/interesting-content-post.php

Would Super Cache end up changing that to http://www.mysite.com/interesting-content-post.html?

…and if so, which version would the search engine spiders see?