You've probably been using the MacBook Pro power supply/power brick with the "stubby" 2-bladed electrical connector.I received this cord with my MacBook Pro 15" (2015), along with the standard charging cord. I have been lugging it around for years. What is it's purpose?
Yes, that extension will work for any Apple brick that has the removable prongs. I use it on my Late 2020 M1 MacBook Pro and it works great!!My new MacBook Pro didn’t come with one. Hoping the older one will fit!