In
Strange Bedfellows right near the end of Season 7 of DS9, the Breen sign up with the Dominion. Turns out the little coolant-suit wearing weirdos have a homeworld that, contrary to popular belief, isn't a frozen wasteland, but is

quite nice. No-one knows why they wear the coolant suits though, they wouldn't even tell the Dominion.
Anyway, their ships are generally small and ****ty, probably a little less powerful than similar Fed vessels, but they've all got these big energy-dampening weapon things that hit a ship and completely drain all its power. Shields, weapons, engines, warp-core, everything dies. Then they use their ****ty photons to just pound the crippled derelicts into space-dust.
Thanks to the Breen, the Dominion absolutely massacred the Fed-Klingon-Romulan fleet when they retook Chintoka. That was the battle where the original Defiant was destroyed.