poor call quality

The power supply that came with my new Obi 100 is defective (unit does not power on, and checked the power supply with a multimeter), so I tried one of those universal adapters, set at 12 volts, 500mA (and . Call quality seemed fine, until my wife made several calls to Canada and told me that there was significant lag, they were talking over each other, and the phone cut out after every few words. I tried power cycling the Obi and that didn't help. I've not come across other complaints about the sound quality, so I'm wondering if I possibly got a lemon (clearly the power supply is a lemon). ISP is Comcast, using a Motorola Surfboard 5100 and D-Link DIR-615 router.

I tried to request a replacement on Amazon, but they'll only do a refund, and the price rose a few bucks since I bought it last week. I don't want to give up on this device yet, due to all of the rave reviews.
Any suggestions?

Thanks