While I don't use a low-powered system in general, a lot of my PCs' big XP awards come through high-level domain achievements.

My adventures focus more on a few major encounters (often very deadly ones) rather than lots of little ones. I find it a waste of my and my players' time to do the "10 encounters at CR x is enough to level up the group of 4 adventurers."

Taking the real time to play out 10-20 encounters for a single adventure is just way too boring for my tastes. That's pure hack and slash. I'm much more a fan of focusing ona few major encounters that are worth a detailed play-through, and as such giving the normal XP awards has NEVER seemed to generous for the significant accomplishment of beating a really tough encounter.

Where the xp awards pile up to fast, by the book, is doing the 10-20 encounters per adventure, wherein the PC's are rarely all that threatened, but the smaller xp awards just keep accumulating until by the end the DM is like, "Wow, that's 18,000 xp apiece. Gee, maybe these xp awards are too big..."

If xo awards are broken down and handed out once per game session or at the end of major encounters, they don't seem so high anymore.