Dum, Dum, Dum dum dum, Dum!
"Money isn't everything, but it's a tie-breaker in Power Grid!"
On your Profile page, under collection, there is an area at the top for games, and below it is the stats for expansions. The counts are there.
As my little collection is growing and my wife is getting more and more worried over the number of games I own, I think it would be nice to be able to see how many of the games I own are expansions and promos.
Perhaps there already is such option but I have not located it yet?