Choosing a laptop AC adapter replacement is fairly easy, but it is important to understand a few terms to ensure you get the proper replacement that is fully compatible with your laptop model. Using an incompatible adapter could cause damage to both the adapter and to your laptop, so it is imperative that you take a moment to understand the main points that differentiate laptop AC adapters.

An AC adapter converts the AC (alternating current) power coming from a wall outlet into DC (direct current) power that the laptop requires. Virtually all AC adapters will support the correct AC current, so the focus should be on finding an adapter that provides the proper DC current for your laptop’s model.

If you look on the original laptop AC adapter for your laptop you will see a number of specifications for the voltage, polarity, etc. for this adapter. You can sometimes find this information on the laptop itself as well. Look on the sticker at the bottom of the laptop for this info. Sometimes this information is also listed near the DC jack where the AC adapter is plugged into the machine. This will often read something like “DC18V 5A (MAX)”.

The first important number is the voltage. Common voltages are 15V, 16V, 18V, 19V, 20V, 22V, and 24V. The second most important number is the amperage, or amps. Common amp ratings are 6A, 5.6A, 4.7A, 4.5A, and 3.8A. It is important that both of these numbers match to ensure compatibility. Both of these numbers work together to produce the overall wattage of the adapter, which is the voltage multiplied by the amperage. So an 18.5 Volt 4.1 Amp HP AC adapter would end up with a rating of 75 Watts.

Another specific marking is the tip polarity which can be found on the brick portion of the adapter. This is a symbol with a + and – sign and a graphic indicating whether the tip or ring are positive or negative. If the positive circle is connected to the small center dot, for example, the adapter has a positive polarity, meaning that the tip is positive and the barrel is negative. Make sure the polarity of the AC adapter matches the laptop; most laptop AC adapters are center positive.

The last important factor of an AC adapter is the size of the tip. If the tip is too small or too large, it will not fit the connection point on your laptop. The tip is most often expressed as a measurement, such as the 6.3mm x 3.0mm tip used on some common Toshiba laptop AC adapters. Generally if you use your model number or the original part number you should not have to be concerned with the tip size.

To simplify the process, you may consider using an online parts supplier which can help you find compatible parts for your laptop model. Armed with the information above, however, you can make a very informed decision and know the part you are purchasing is compatible with your laptop.