Check out the old original adapter to get detailed information regarding the specifications of the AC adapter, which is very important. Or you can also refer to the instruction booklet. Generally speaking, your desired adapter is available in the market. If you can't get the exact match, then please ask an expert for advice and choose an alternative one.
AC Adapter for HP Compaq Presario CQ56
This information could be found on your adapter box,DC18.5V and 65W Max power are quite important factors when you made the order.
As a professional seller,from our previous experience,you could just search the charger webiste with the model of the laptop or the P/N number,you could get a right adapter as your original one,and then check the following information of the advertise,check the Input, Output and the power information ,you will be in confidence of a quite correct ac adapter.
One thing to remember is that the more closely the new adapter matches to the old one the better it will perform. If you have some basic knowledge about power adapters and know how they work, you will be easily able to find a proper adapter for your device.
As long as you follow the above tips, you will find it much easier to choose an adapter. Your adapter won't last forever. Don't hesitate and replace it when it's necessary. A proper ac adapter can enable your device to function well.