Hi,
It will sound differently likely, for a few reasons. The headphone on your laptop is connected to the chassis, so any moving parts, fans, etc are all connected there and will share noise. Going to a USB DAC cleans that up. The other reason is not so much the DAC (since you could easily end up with he same DAC chipset or something similar quality actually) but actually the output amp stage that is used as depending on what they use, these can color sound or simply be better quality than whatever your laptop is using. So you would be looking at a USB DAC/AMP combination unit, or two separates (DAC and AMP). The other factor is the quality of the recordings you're listening to (and lossless doesn't matter, I'm referring to the actual recording being high quality and not just poor quality recording at a high bit rate in a lossless container). So if it sounds good now, it should sound cleaner, less noisy, and maybe just overall better if you get a dedicated system. But will it be night & day? Maybe not, depending on what it is right now (can't say without having heard it or seen measurements of your laptop's output).
Very best,
