MagSafe adapter, but just in case you can't seem to find the value in said feature, the $11.99 MagStay Pro is out to remedy your curious quandary. As with the JerkStopper, this concoction actually plugs into your MBP's nearby USB port in order to get a better grip on the machine. Apparently, this thing is designed to help you avoid any "unintentional disconnections" in power, but aside from totally blocking your USB port (no passthrough?), you're also begging for some extraneous repair bills. To each his / her own, we guess.