Laptop charging and not charging intermittently

Hi, My laptop when plugged in is charging for a few seconds then not (as if i had unplugged the charger) then a few seconds later it charges again, and this repeats constantly. I have previously had this issue about 4 months ago and I returned it to acer as it was under warranty. They sent it back to me having told me they had replaced the charger (I new this wasn't the case as i had tried buying a new charger and battery. Anyway I am now once again having this issue so does anyone know what might be wrong and how i could fix it? as my laptop is no longer in warrenty