There is no definitive answer because non-Volvo anti-freeze will probably
work just fine.

The main difference is Volvo engineers were probably involved with the
chemistry used in the Volvo fluids and I assume they extensively tested
it against the metals in Volvo engines (and real world has tested
it over millions of miles of actual use). So you know it works. It's
$20 a gallon and you won't need much. I use it in my 850 and S70 (but
I am also close to a dealer so it is not difficult to get a hold of).