From the Basic Game manual:

You can spend 5 XP to do the following:
* Replace an existing Distinction with a new one.
* Add or replace a Limit in a Power Set.
* Switch two Affiliation traits.
* Unlock a minor Event resource.

You can spend 10 XP to do the following:
* Add a new SFX to a Power Set.
* Step up a d6 or d8 power trait by one step.
* Add a new d6 power trait to a Power Set.
* Remove a Limit from a Power Set that has two or more Limits.
* Unlock a major Event resource.

You can spend 15 XP to do the following:
* Step up a d10 power trait by one step.
* Replace an existing Power Set with a new one.
* Add a new Expert Specialty or upgrade an existing Expert
to Master.

As a player, you always have the option to spend 1 XP to add a Plot Point to your current pool of PP. This also increases the minimum PP you start each session with by +1 to a maximum of 5 PP (with 4 XP spent). It’s not the most efficient use of your XP, but maybe you really want to get ahead of the game! This increased minimum starting amount resets to 1 at the beginning of a new Act, though -- make use of ‘em while you’ve got ‘em.

More coming soon...