Chargers not working?

Hi, I've been having trouble with my iphone/ipod chargers. I've been using the ones that came with my phone/ipod for the longest. And eventually they started to degress and I would have to position them a certain way so they could charge, so I thought "ok time to get a new charger." So i get a new charger (cheap generic one from walmart) and after a few days it started doing the same thing. I would have to position the cord a certain way and it started showing a yellow caution sign and it said "charger not supported with this accessory" It does this with all my apple products, and its even done that with old chargers I've found that worked just fine before. Is there something wrong with my devices? Am I just using cheap chargers? What should I do?