Do we need to get certified from UL if we have certified from IEC to sell a electric/electronic product in the US market?
Generaly speaking, UL is not mandatory (as isn't TÜV for instance) but it may be requested by certain markets specificaly if there are national deviations in some states that were not specifically covered by the mentioned standards. You may consider the CB scheme for your product(s) as an additional peace of mind. UL may be seen however as an advantage if your big clients demanded it as some will refuse products if there is no UL or CSA certificate on request.