27” Cinema Display

A1316 or A1407?

For the A1316: LED Cinema Display (27-inch) Manuals and Downloads - Apple Support

For the A1407: Apple Thunderbolt Display (27-inch) Manuals and Downloads - Apple Support

The grouped cable with three plugs: The Mini DisplayPort for video connection to the computer; MagSafe-cable (up to 85 W) for charging laptop through the monitor (optional); USB 2.0 cable passthrough to use the (extra) monitor USB ports with the computer (optional).

Urquhart1244 wrote:

A1316 or A1407?

For the A1316: LED Cinema Display (27-inch) Manuals and Downloads - Apple Support

For the A1407: Apple Thunderbolt Display (27-inch) Manuals and Downloads - Apple Support

If the display is a Thunderbolt Display,

• The hydra cable will have only two heads: Thunderbolt and MagSafe. This is an old form of Thunderbolt that lives on Mini DisplayPort connectors.
• The monitor will have downstream FireWire 800 and Gigabit Ethernet ports.
• You will need an Apple Thunderbolt 3-to-2 adapter instead of a USB-C (DisplayPort) to Mini DisplayPort one.

The OP mentioned three cables coming out of the display – which would indicate that it is a LED Cinema Display.

It is not enough to pick an adapter whose physical connectors "fit". Each display is expecting to see a particular type of signal ("DisplayPort" or "Thunderbolt") on its "Mini DisplayPort" connector, and the adapter needs to be one which will deliver that type of signal.

They connect to the relevant ports and they can only fit in one type of port.

That would be (from left to right), USB (to enable the USB ports on the display), Mini-Display port (for video) and Magsafe (for charging the connected computer).

On current Macs, you would need an adapter to go from USB to USB-C on the Mac. From Mini-Display Port to USB-C or HDMI on the Mac, and you would leave the Magsafe connector unplugged as it cannot be used.

Urquhart1244 wrote:

USB 2.0 cable passthrough to use the (extra) monitor USB ports with the computer (optional).

You probably need to plug this in if you want to be able to control the brightness of the monitor. Apple seems to be fond of making monitors that are software-controlled and that have no physical controls on the monitor itself.