Preparation
Before starting to install Ethernet Splitter, there are several things that you should prepare, such as

• A pairs of Ethernet Splitter. Since, there are two model of Ethernet splitter available on the market. First, the splitter which has 2 RJ-45 ports (RJ-45 Female) and 1 RJ-45 Connector (RJ-45 Male). The second one, the splitter which has 3 RJ-45 ports (RJ-45 Female). 1 on the front side and 2 on the backsides. (read more about Ethernet Splitter Models here). So, make sure you have bought the right model of this device. If you have wall outlet on you cable installation which actually has RJ-45 Female, you have to buy, the first model of splitter. But, if you don’t have wall outlet or the each end of your Ethernet cable are using RJ-45 Male, you have to buy the second model. Please remember, you have to buy a pairs of Ethernet Splitter. If you don’t, it will not work.
• 4 (four) piece of Ethernet Cables. Make sure the cables have RJ-45 Connector (RJ-45 Male) at each points.

Installation Steps
Before we begin on installation steps, you can see the following figure which shows you the Ethernet splitter installation diagram. Use this diagram to help you installing this device.

Click on image to enlarge

If you are already have those requirements mentioned above, follow this steps install Ethernet Splitter:

1. First, we work on the first splitter which will be connected to the hub or switch. So, we need to use two Ethernet cables.
   • Plug the first cable onto the first port of the splitter then plug this cable also into the hub. Do the same step two the second cable. So, you will have two network cables that connecting the hub into the splitter. (Number 1 on the image above)
   • Plug the splitter cable (which is has RJ-45 Male pre-installed) to you wall outlet (if you are using wall outlet and you cable is behind the wall). (Number 2 on the image above)
     However, if you don’t have wall outlet, you can use a splitter which has 3 RJ-45 ports (The second model that I mentioned on Ethernet splitter models post). You have to plug you network cable that is already used on you previous network installation.
   • You have done installation for the first splitter. Now, go on to the second splitter which will connect you computers.
2. Now we work on the second splitter. It also needs two Ethernet cables as the first one.
   • Plug the splitter cable (which is has RJ-45 Male pre-installed) to you wall outlet (if you are using wall outlet and you cable is behind the wall). (Number 3 on the image above)

     If you don’t have wall outlet, you can use a splitter which has 3 RJ-45 ports (The second model that I mentioned above). You have to plug you network cable that is already used on you previous network installation.

   • The last thing that you should do is use the rest two of Ethernet cables that you have prepared before and plug them into both of the splitter ports. Next, plug those cables to each of your devices or computers. (Number 4 on the image above)

Everything done. Now you have to configure network setup on your computers and router. Then do some network connection tests in order to make sure both computers connected into network.

Models
Basically, there are two models of Ethernet Splitter which can be found.

1. First, the splitter that has 2 Ethernet ports (RJ45 Female) and 1 cable with RJ-45 connector (RJ45 Male). This model usually used for those who has a RJ-45 wall outlet on their Ethernet cable installation. See the following image for more detail.
   
2. The second models has 3 Ethernet ports (RJ45 Female). 2 female ports on the front side and another one on the backside. This model usually used for those who does not has a RJ-45 wall outlet on their Ethernet cable installation. In other hand, this device used if your Ethernet cable have RJ-45 Male at both of it’s end point. See the following image for more detail.
   

Which one that you should use is depend on what type of Ethernet cable installation did you already have.

Popular Products
As we search at Amazon, there are several Ethernet Splitter splitter products that available on this site. We have selected some products which received a number of reviews and rating from the customer. Here they are:
Cables to Go 37133 2-Port RJ45 Splitter/Combiner Cable
Product Description: This item has 2 Ethernet ports (RJ45 Female) and a single cable with RJ-45 connector (RJ45 Male). This item sold individually. This product covered by lifetime warranty.
Amazon Ratings: 2.6 out of 5 star ratings
Amazon Customer Reviews: 90 reviews
Price: $9.99 (single unit)

HDE RJ45 Ethernet Splitter
Product Description: This item has 3 Ethernet ports (RJ45 Female). 2 ports on the front side and another one on the backside. This item sold individually. So, in order to working properly, this item must be used in pairs for each installation.
Amazon Ratings: 2.4 out of 5 star ratings
Amazon Customer Reviews: 49 reviews
Price: $1.52 (single unit)

Premium 12-Inch RJ45 Splitter Adapter
Product description: This item has 2 Ethernet ports (RJ45 Female) and a single cable with RJ-45 connector (RJ45 Male). All 8 pins are connected straight through. This item sold individually. Comes with 1ft cable. Covered by Lifetime Warranty
Amazon Ratings: 1.4 out of 5 star ratings
Amazon Customer Reviews: 5 reviews
Price: $2.98 (single unit)

Cables Unlimited UTP-4000 Cat5e Pair Splitter Adapter
Product description: This item has 2 Ethernet ports (RJ45 Female) and a single cable with RJ-45 connector (RJ45 Male). This item sold in pairs.
Amazon Ratings: 4 out of 5 star ratings
Amazon Customer Reviews: 10 reviews
Price: $20.43 (in pairs)

Some points you should remember before purchasing Ethernet splitter are choose the one that meed your need or according to your existing cable installation, as mentioned above. The second point, Ethernet splitter will only work if it used in pair. So, make sure you buy a pair of it.

What is Power Over Ethernet (PoE) Splitter?
A Power Over Ethernet (PoE) Splitter is device which transferring electrical power together with data securely through a single Ethernet cable. On the other hand, this device is using only a single Ethernet cable to supplies a DC power as well as supplies network connection to a network device like router, Wireless Access Point, etc. See the following picture to know how does this device looks like.

Click image to enlarge

From what that have mentioned above, the function of Power Over Ethernet Splitter is totally different from an Ethernet splitter. As we know an Ethernet splitter is a device which enables two computers or 2 network devices connected to the router only using a single Ethernet cable.

According to IEEE standard for PoE, to use this device you need to use CAT-5 or even higher version of Ethernet cable, such as CAT-7. However, for low power levels this device still able operate with CAT-3 Ethernet cable.

Where Can I buy a Power Over Ethernet (PoE) Splitter?
PoE splitter may available in most computer spare parts shop. However, if you decide to buy it online, Amazon.com might be the first place you can visit. There are a wide variety of PoE splitter brands available on this site, for example D-LINK, TRENDnet, TP-Link, Cisco, PowerDsine and many other brands.

More info about PoE technology, please visit Power over Ethernet page at Wikipedia.

Images from D-Link DWL-P200 Power Over Ethernet Adapter