|I'm, surprised the adaptor plugs fitted both Dell and Toshiba laptops. They're usually different sizes. You're lucky. ;o)|
I doubt there's anything to worry about.
The power difference is marginal. You may find this mains adaptor unit runs just as hot when used on your wife's laptop - unless hers is a small netbook, or of a newer design which requires less power. Try it.
Manufacturer-supplied adaptors are pretty robust and will happily meet the requirements for most conventional laptops, regardless of make.
(cheap Chinese replacements are another matter)
However, a dedicated netbook adaptor would struggle to power a conventional laptop. Many netbook PSUs are only rated around the 40W/2.5A range, and would be heavily overloaded if attempting to power something that required a beefier PSU capable of around 65w to 90W at say, 3.5A to 4.0A.