Everyone knows the problem: you're on the go because you've arranged to meet colleagues for dinner and you didn't check whether your mobile phone has enough battery left. 
Hotels in the USA hardly offer any adapters to borrow anymore. Accordingly, this adapter should always be included in your luggage. In addition to the Universal Adapter, this small version is available in the Cabin Crew Store and is an absolute must-have as it easily fits in a handbag.