Can two different complexity classes be equal relative to an oracle? Example request

Question

Is there a known example of two complexity classes, $A$ and $B$, such that:

1. $A \neq B$;

2. there is an oracle $O$ for which $A^O = B^O$?

I strongly believe that there are such examples, as otherwise $P = PSPACE$ (note that $P^{PSPACE} = PSPACE^{PSPACE}$), but I was looking for an example of this.