Ring Pro directly to transformer

I recently purchased a ring doorbell pro. I have a very old existing doorbell, however it's not worked for a long time. That is to say I don't think the chime works anyway and I'm not worried about it working. So I pulled new wire through from my old doorbell to the transformer. So I was going to connect the Ring Pro directly to the transformer. There are a couple possible concerns though. First, my transformer is putting out 25.3V so a little higher than the 24V listed. Upon researching to see if this slightly higher voltage is a concern I came across the next concern. I've found multiple posts/articles that mention you can't directly wire to the transformer without something else inbetween. I've read different things though I've seen some posts that say I need a resistor, others say either the Pro Power Kit or the Advanced Power Kit. Thoughts?