As you have not said exactly what model NSPIRE your original unit was I cannot be 100% sure but I would say probably not, or certainly not without confirming a few things.
The B86 requires an adaptor that provides 19.5v and is able to deliver up to 6.15A (120watt) of current. So you will need to check the adaptor on the first unit, if it is also 19.5v and can provide 6.15A of current then yes you can interchange, however if the current provision is less than 6.15A then you must not use this adaptor on the B86 as it will not be able to provide the required power and could damage the unit or power adaptor.
So it might be you could end up using one adaptor on both units because the B86 one is good for both but not be able to use the nspire one on the B86.
You will need to check voltage and current of both adaptors.