When I plug the AC adapter into my DELL VOSTROO 1000 laptop, it doesnot charge. the only message i get is ' plugged in, not charging'.

It is possible the charging plug socket on the computer is defective.

It seems that the your power adapter does not have correct amount of power.

the old power supply must not be putting out enough power to charge

Could be many things, not necessarily in this order, but the ac adapter has gone bad(highly suspect), the power converter/charge board has gone bad, the power plug receptacle has an intermittent break in it from years of use (might be able to re-solder that one back on the board ) - or the new battery is not as new as you thought. In any event, You should send it to an authorized repair center - looking at a $100 bill or more.

As you say the system is 4 years old update the bios
your download link is here!
IMP. Be sure to plug in the battery and it should be charges above 10 % and the system should be connected to the mains power supply also ensure there will not be a power outage during the update process
this will resolve the issue 100 %
Dont forget to say thanks!

1. remove all external peripherals 2. try to use ac adapter alone check if laptop will power on. 3. put back batt in with ac adapter. 4. check bios (power on laptop keep tap on F2) 5. check for the bios version, battery info and battery health. 6. check if batt is 0% or 10% charge 7. check battery health and info if the ac adapter is determine or not. also check if batt is performing normally. 8. if batt has 10% charge then download the latest bios for your system. download it from support.dell.com

Schematics for Dells are generally unavailable.
The not charging is normally due to a failure on the charging circuit or damage to the power plug (If ac adapter will not run system or if you have to play with the power connection.)
Replacement motherboards start at about $75
http://shop.ebay.com/i.html?_nkw=dell+inspiron+1000+motherboard&_sacat=0&_trksid=p3286.m270.l1313&_dmpt=Motherboards&_odkw=dell+1000+motherboard&_osacat=0

It probably has the wrong adapter then.

check power supply see if its putting out voltage to laptop

The Dell 1501 ac adapter (possibly other Dell’s as well) has been known to be problematic because of its lack of a plug to jack secure fit. You will notice that the plug can all too easily be pulled from the jack, as opposed to other systems where the plug fits more securely onto the jack. The plug and jack combination is poorly designed so that over time, the plug will come unseated depending on how much movement the machine is subjected to. This will result in power error messages or outright power-up failure. So before assuming you have a faulty adapter, make sure that it is not just a loose plug that is causing the problem. If you look inside the jack, you will notice that there is a 3mm region of non-conductive material nearest the surface of the jack. Use a strip of standard electrical tape 3mm wide and long enough and wrap it around the base of the plug (you may need more than one layer of tape to get a good fit). I have used this method to secure my plug and it has served me well. If the tape comes undone over time, just simply replace it. A more “elegant” method would be to use an “O” ring of the appropriate size (about 6mm) around the base of the plug in lieu of the tape.