I don't know about Gateway, but most laptops these days use the same DC power supply. I have three here and they all use 19V. You just need to check the polarity, though I doubt that'll be a problem. Sounds as if your power supply has failed, not an uncommon occurrence here. Is there a warning light on the transformer and is that working? A common problem is the low tension cable breaking internally where it joins the co-ax plug that plugs into the laptop, particularly if you pull the cord out by the cable rather than the plug. But also check the mains lead that goes into the transformer as that can fail, again especially if you pull it out by the cord and not the plug.
If you need a new power supply Julian at CSM2000 on Middle Street (San Pedro) should be able to help.