Albus Dumbledore's forceful spell

"Dumbledore flicked his own wand: the force of the spell that emanated from it was such that Harry, though shielded by his golden gaurd, felt his hair stand on end as it passed and this time Voldemort was forced to conjure a shining silver shield out of thin air to deflect it. This spell, whatever it was, caused no visible damage to the shield, though a deep, going-like note reverberated from it-an oddly chilling sound."

- description of the spell

This spell was seen once used by Dumbledore in the Ministry of Magic, during the Battle of the Department of Mysteries on June 17, 1996, while he duels with Voldemort. This spell was told to be very very powerful since when Dumbledore casts this spell, Voldemort can't bear the power of it so he conjures a silver shield to deflect it. But when the spell hits the shield, 'a deep, gong-like note reverberated from it-an oddly chilling sound. Though, this spell didn't really cause any visible damage to the shield which aslo tells that the shield's power is nearly the same as Dumbledore's.