Ring of Psionic Assertiveness (3.5e Equipment)
From D&D Wiki
Ring of Psionic Assertiveness: This ring is made of silver with veins of crystal running through it, the ring has a enchantment/has been psionically empowered in such a way that it makes it harder for others to resist the powers of a psionic character wearing it. It does this by boosting the manifester's assertiveness/confidence/resolve and in doing so makes it harder for others to resist their powers (this does not lower the enemies modifier to pass, just increases the DC).
If two Rings of Psionic Assertiveness are worn the effect does stack.
Effect: All powers manifested by a psionic character add +1 to the required Will save DC, as if the wearer had an extra +1 to their INT modifier (though the wearer's INT is not actually brought to the next modifier in any other respect). Any psionic powers that do not have a Will save are unaffected by this ring.
CL ; ; Market Price: 2,500 gp