Q: does a replacement charger run the risk of killing power supply

I have an ibook g4 and i just had to buy a new battery but it won't charge...the old one wasn't charging at all, and the new one won't either...i had to buy a replacement charger a few years ago, then about 4 months after that the computer stopped working.  When i brought it to get fixed, the man had an original charger and said the computer worked fine when plugged into that, but he never used the charger i supplied...should i ebay an actual charger that goes with it? the computer works fine except this power supply problem, first it would shut off after a day, then it would only last an hour, then 20 minutes, then sometimes only work when the battery was out and charger plugged in.  now it won't even do that...HELP lol, i don't wanna get rid of this computer!(i use a mac mini now, but want my laptop back)