Look on the power adapter that you currently own. The label should have two parts, one that says input and the other output. Under the outpu, you need to know the voltage and aperage that it provides.
The important part is the output. Go onto ebay, & look for an AC adapter that has the same power output as the one you have. If you cannot find the EXACT same output, then make sure the Voltage is the same (too much V and you can cook the mother boad, too little and it won't work) and make sure that the amperage is iqual to or greater than that of you current adapter (the laptop will only draw the current that it needs, if the adapter's delivery is to low, then you may cook the adapter).
For example the one for my tecra says
Toshiba
AC Adapter
Model: bla bla bla
Input: 100-240V~1.5A 50-60Hz
Output: 15V 4A
Therefore in looking for one for my tecra, I would want to find ione that has an output of 15V and at least 4 A (pay attention, sometimes they list the amps in mA; 1000mA is the same as 1A). By getting a Toshiba one (even off ebay) you can be pretty sure that the plug will be the same and have the correct polarity, but check it before plugging it into your laptop.
