Xiao Bei Baihuo (小北百貨) is a household goods chain that sells almost everything (dishes, mops, detergent, stationery, food), at reasonable prices. They are all over the city (at least ten locations), and the prices are generally cheaper than the big department stores like Carrefour and RT Mart. They are crowded, with narrow aisles and stuffed shelves, but these little mini-department stores are worth the visit. I believe they are all open 24 hours.

A more detailed description, as well as a picture of a storefront, can be found at: http://tainancity.wordpress.com/2010/08/06/everything-store-xiao-bei-bai...

Locations:
After bringing up Tainan City on Google Maps, cut and paste the store name (小北百貨) into the Google Maps search bar, and all of the locations will pop up. From there you can zoom in to the store closest to you, and find the best way to get there. Travelling down the street, you should be able to easily spot the four symbols that make up the name, usually in large red lettering on the storefront sign.

Their website (Chinese) also lists the locations, and has online flyers available for viewing: http://www.small-north.url.tw/