Oh my, I've never heard of duck sauce, but my trusty google makes it look like they are so very similar. In Canada we call it plum sauce and it's almost always served when you order chicken.
Yeah, when I googled plum sauce duck sauce also came up as well... here when you order Chinese food duck sauce is served with the egg roll, spring rolls, etc. usually. It's basically like a fruity sweet & sour sauce. I've seen it served with chicken and other dishes, but most commonly with spring rolls and appetizer-type stuff.