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Recently I lost my LG-27GP850 monitor power adapter which was 65w (19v, 3.42a). I could not find same tip size & watts power adapter. That's why decided to use other companies original adapter but different tip size. ☹️
Now I just need to know, can I use 5.5x2.1mm female connector on 5.5x2.5mm male tip?
If you truly mean "use 5.5x2.1mm female connector on 5.5x2.5mm male tip" then the answer is no: the 2.5 mm diameter pin in the jack is too wide and the 2.1 mm socket in the plug won't fit onto it.
If, however, you got your genders mixed up, and you really mean "use 5.5x2.5mm female connector [plug] on 5.5x2.5mm male tip [jack]", then, yes, it will fit. But it may not make a reliable contact, as the pin in the jack relies on the sideways pressure to touch the socket in the plug. (The plug in your first picture is a female: hole = vagina = female.)
Regardless, be aware that there is no standard for positive center or negative center. DO not blow up your product with the wrong polarity voltage.
The best answer is "maybe", because the plug in the picture you provided (connected to the AC adapter), looks to be of the kind that would not work with a 5.5x2.1mm jack, but many such power supplies come with plugs that work with both 5.5x2.5mm and 5.5x2.1mm jacks.
See this answer for examples of compatibility, and about the problems with using genders to refer to these kinds of connectors. (The OP and I call that plug "male", while another poster calls it "female". There is enough real-world usage of both labels that neither can be called right or wrong at this point in time. As a result, the overall consensus is to just call them "plugs" and "jacks" instead.)
Also, as another poster noted, double-check the polarity of your power supply. While the consensus is to have the outside of the plug be negative (actually "ground") as shown in your picture, they would not put the picture of it on the device if there were not other devices that expect the outside to be positive.
