Hi Venkat,
If you want to use the dropdown widget to select from a single list, you will have to have one attribute that contains all the desired values. If you are using enumerations, you will have to have another enumeration with all values (TV, Laptop, Desktop, Phone, and all the values for 'other) and as soon as a user selects either Phone, TV, laptop, or one of the 'Other' values, then you must set this value behind the scenes using an on-change microflow. It does mean that you will need to maintain separate enumerations, but it will give you the UI you are looking for.
Best,
Rob