If you're looking to replace a lost or broken laptop charger, you could turn to the original manufacturer to source a direct replacement - or try a universal adaptor solution. This might be easier to track down, and may even have the advantage of being lighter or more compact than your original.
The FSP NB Plus Universal Notebook Adapter comes from power supply specialist FSP Group, and is certainly reasonably compact, measuring 154x74x17mm. And with all its detachable cables in place, it weighs 431g, or only 224g without.
On one end the FSP NB Plus takes a standard figure-8 mains lead; on the other a cable to which you can connect a variety of round plugs of different sizes for various brands of notebook computer. Brands supported include Acer, Asus, Dell, HP, Lenovo, Sony and Toshiba. That's not to say that every model from every brand is supported - there was no adaptor for the older Apple PowerBook power socket, let alone the new MagSafe version.
In addition to charging your laptop, you can also take adavantage of a powered USB port on the side, useful for topping-up iPods and mobile phones that are designed to be charged by USB power.
To set up for your model of notebook, you just need to find the correct size of plug, and set the required voltage. This information is usually printed on the underside of the laptop, typically a figure between 15V and 21V DC. To adjust output voltage, a sharp point is necessary to depress two recessed buttons marked Set and Adjust. Most pens are too thick - you'll need something more like a cocktail stick. Also here is the option to display internal temperature in degrees C or F.
The NB Plus Universal Notebook Adapter is specified to supply up to 4A at the lowest voltage, down to around 3A at 21V. This gives a maximum power output of around 60W, which is fine for most laptops. Larger or older desktop replacement laptops may require more power though, sometimes upwards of 80W, in which case this adaptor could have difficulty in fully charging a flat battery while the laptop is in use.