https://www.amazon.com/dp/B095YCKBN8?ref=fed_asin_title
The main thing it needed to be (2.5 amp 120v) was 30VA, making it big and heavy. I think the original A16 (not the ultra) was 1.5 amp, but I believe it still needs to be 30VA. Maybe someone can verify this.
As long as that link is still live, and you live in the USA, you can confidently grab it for your 2nd-hand A16ultra purchase

Cheers!