I know that fear stacks but i always thought it must be from different sources so i can't demoralize by intimidation checks the same target or can i?
When you spam Imperious Command to Demoralize it applies a "higher" effect even if it didn't stack.
Now if you didn't have Swift Demoralize, Intimidate effect would just be Shaken off your effect and yes WotC has generally used same source = nonstacking even through it's a spell-based rule. This is why you stack it with something else like the Dreadful Wrath
PGtF and Frightful Presence
Draco and Mortifying Attack
FR:CoR Feats, Grafts like Frightful Crest
RotD, various Spells through Blade of Fear & Pain
LM/SpC probably deserves a mention, and Class Features that reduce Saves improving the effectiveness as well as the overall total debuff effect like a Paladin of Tyranny's Aura of Despair
UA, a Bound Focalor's Aura of Sadness
ToM, or a Hexblade's Dark Companion
PHB. Through a lessen known bonus is the Thayan Slaver
FR:UA which for a two level dip can deal 1 Wisdom Damage with each usage of Intimidate.