I can think of several different ways to add a second external monitor. Not all of them will work on your laptop – that depends on your machine’s capabilities – but some will.
Let’s look at your options.
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Use your additional video outputs
The easiest approach is to see if the machine itself has additional video outputs.
For example, you currently have your main screen and another monitor presumably plugged into an adapter that’s available on your Acer. If there’s another adapter available, then you should be able to plug in an additional monitor.
But I’m going to assume that this is not the case for you (because you wouldn’t be asking the question). So, let’s look at your next option.
Try a USB-to-DVI video device
A very quick, easy, and inexpensive solution is to use a USB-to-DVI device.
My desktop has two video outputs and I had monitors plugged into both of those. I wanted to put a third monitor on my desktop machine, so I purchased a USB-to-DVI device. I plugged it into the USB port on my desktop and the DVI input on my monitor. My machine reconfigured itself automatically and then I had three monitors. It worked quite well. This method is also great for presentations or if you’re taking a laptop to various locations and you have no other way of connecting an external monitor.
The only caveat is that the USB-to-DVI device works great if you are displaying static or slow-moving images, such as web pages, documents, or photos. It may lag with motion video or anything that’s heavily motion-oriented, like a game. The USB interface simply can’t transfer the data fast enough to keep up with things like that.
When I used it, I only had a problem with video on the monitor that was connected to the USB. The other monitors displayed everything fine. I even played World of Warcraft on them, but I was never able to play it over the USB interface.
Use the display port or HDMI
Some laptops now include additional ports called “display ports.” For example, my Surface Pro and my MacBook Pro both have this output.
Some laptops also have HDMI. That’s another alternative because it includes both video and audio. Quite often, you can use those in addition to whatever you’re using normally.
Using the display port or the HDMI port depends on the hardware capabilities of the laptop. Does it have those ports? If so, then it boils down to the capabilities of the installed video drivers. If you’re having problems with that, make sure you have the latest drivers.
For both the MacBook and the Surface Pro, all I had to do was plug in a Display-Port-to-HDMI adapter for my monitor and it worked really well.
Get a new video card
There is one more scenario that I want to describe. With your laptop, it might not be feasible, but it will work on some desktop machines.
Some video cards can handle multiple monitors. If your desktop allows you to have several video cards plugged in, you can connect multiple monitors. Windows handles this just fine. If you’ve ever seen flight simulator scenarios where they have nine monitors displaying portions of a very large visual field, they’re using multiple graphics cards to display that image.
So, those are my suggestions for you. My guess is that if you have an older machine, the USB solution is probably going to be the most practical and the easiest to set up.