I have seen a "Universal Laptop Adapter" sold in a computer shop before. I am thinking of getting one for a laptop. Is it safe to use? What differences are there between one of these and a typical laptop adapter?
The short answer is Yes and No.
Sorry it is that messed up. Too Many Brands, Too Many false claims. Targus and Belkin make great adapters for example but the switch models regularly and so the one that worked with your computer last month may not be available this month.
Best bet is to hit The Targus Power Store click on laptop, then on the page that pops up select your make and model and see if tips exist for your computer. If they check the numbers of the matching adapters on the right and call a few local stores to see if anyone has this model in stock, it will work, Targus is thorough.
If not contact the manufacturer, they can usually get you a proper replacement for a similar price but can take several weeks depending where it will come from.