Dunno about the A3000, but I replaced the one in my A4000 last year which was an 80mm fan, but I can`t imagine them being different sizes given CBMs love of cost cutting and standardising parts.
Two things to note though..
1. Be very careful inside the PSU, even when turned off they can hold enough juice to do you some harm.
2. Make a note of which way the old fan turned, ie. did it suck air in, or blow air out ?
