As funnybone wrote, kollels usually give a stipend. There are some that don’t give any stipend, and some that give a very small amount, and there are others that give more. A lot of it depends on location (Eretz Yisrael, Lakewood, out-of-town, New York), but it also depends on the specific kollel.
Nowadays, I think it would be very rare or impossible to find to find a kollel that pays enough to live on, but whatever they do give is definitely needed in combination with the wife’s salary. Often, the couple/family is only able to manage due to the kollel stipend combined with the wife’s salaray.