If you talk about an experience in your PS that is also listed on your application experiences, you should talk about it in a different light. The key is to not repeat any information anywhere in your application file.
My PS was an EC that was included in my AMCAS application, but I did NOT make it one of my 3 meaningful uses. It's implied that if it's your PS, then it's pretty significant and meaningful. I didn't have much more to expand on it as this EC was a major theme in my PS so I instead used 3 other significant experiences to expand on!