Up until recently Antec's EarthWatts were made by Seasonic. Sounds like you just got a bad batch. I've got an EarthWatts 380w powering a Radeon 4850 Pentium dual-core rig with no issues.
Not had any issues with mine until now, but I am powering a Q6600, 2 hard drives, two optical drives, a sound card and an overclocked GTX 460, so maybe I'm running it a bit close to the max wattage.
I plan to get a new PSU at some point to give me some more headroom for upgrades later, and also have modular wiring so my PC's insides don't look like an explosion in a spaghetti factory.
Going back to my problem I reckon the issue was something to do with power - don't know if it's a dodgy connection or just not enough from the PSU - because it looked like the card was deliberately clocking itself down to 50% as though it was going into a limited power mode.