It's 50. The school sites are always accurate. Last cycle I noticed a few differences between the portal link's instructions for some schools, and what the schools actually expected you to do.
On the Supplemental Information link on AADSAS for Pitt, it says that the supplemental fee is $35, but it's $50 on their official site. It's probably safer to go with the official site, but was wondering if anyone else ran into this.