In Belgium, breweries are often loose with beer categorization. Some don’t bother with style names at all. Generally, a Tripel will be slightly sweeter, smoother, and with a richer mouthfeel. A Belgian Strong Ale will be lighter in color, with a dryer finish. There is a lot of crossover between the styles. If you need a benchmark, think Westmalle for a classic Tripel, and Duvel for a classic Belgian Golden Strong Ale.