Does a laptop computer charge faster when off?

No one answer fits all, it really depends on the laptop!

Some have built in features (vendor specific) that speed up the battery charging, others (including most of mine) charge a lot slower when in use.

Again, no one answer fits all.

It depends on the power supply. We have a few computers which can be run off a lower-wattage power supply while running - it will not charge the battery at all. If you attach a larger power supply, then it can charge and run.

Check with your laptop manufacturer. It seems somewhat common to see power supplies with different wattage being offered. The power supply with a higher wattage may be what you need to charge quickly and power the system while on. Check to see if a larger power supply is available if you need to charge quickly while using the system.

My laptop charges faster when it's turned on for some reason. I think this has to do with heat, as you turn your laptop off the fan stops spinning too so the heat from the core components (mostly CPU and GPU) can now easier spread to other components such as the charging electronics. That's what the fans also are for, not only to cool the CPU and GPU but also to stop heat from spreading to components which can't take as much as your CPU and GPU. I've tried this on multiple occassions and it's always like that, except when it's cooled down and i start to charge it.