You can use a compatible higher or lower wattage adapter without issue, but it won't make your computer charge slower/faster or operate differently. Your power adaptor should provide a steady voltage over a range of current.source
It may only slow your laptop when your voltage is too low or to high, which can lead to odd and unexpected behaviour and it may damage your equipment, but not the current.
However when energy consumption is too high (it doesn't charge quick enough and it drawing energy too much), it may heat up or melt power supply or cord and shorter lifespan of your power adaptor and may lead to operating system stability problems or crashes. See: Laptop power supplies, does current matter?
Troubleshooting on Windows
Potential reason that your laptop may slowing down while charging is because of switching into different computer's power settings, so your laptop could behave differently and overheating, or some applications are activated only when you're charging (anti-viruses, disk compression tools, etc). To check or adjusting these settings of your Power plans, go to Control Panel (list all the items), and select Power Option. You may create your own Power Plan (Create a Power Plan). See: FAQ - Power plans
You can also investigate the issue by running Power Troubleshooter (Power in Control Panel). See: Laptop overheats when plugged.