relay power ratings - AC vs DC
When the relay opens it will draw an arc. With AC power the current drops to zero 100 or 120 times per second (depending on whether you have 50Hz or 60Hz power), and this will allow the arc to extinguish. With DC power you don't get this automatic interruption, and an opening arc may last longer, burning the contacts in the process. That's why relays are allowed to switch only a fraction of the AC power if DC.
It's not uncommon to see 250V AC relays only rated for 30V DC.