Connecting two wireless adapters to the same computer will not improve the system's Internet connection speed. Adding a second Wi-Fi adapter to a computer will improve the Wi-Fi performance if the second adapter features a better-performing standard, but it's overriding the older, slower card, not working in conjunction with it. The Internet connection speed is usually bottlenecked at the service provider level and the Wi-Fi connection has enough bandwidth to support all of the available Internet speed.

ISP Speed Restrictions

An Internet connection is only as fast as the slowest part of the network. A faster Wi-Fi connection is unable to obtain a faster Internet connection speed than the service provider allows. The ISP's network can only support Internet connections as fast as the infrastructure can technologically support; however, the actual speed you get is typically much lower and artificially capped. ISPs often sell multi-tiered Internet connection speeds where you can pay more to have a faster connection. Adding more or faster Wi-Fi adapters to the network won't improve Internet speed because the bottleneck point occurs earlier in the connection chain.

Adapters and Routers

If you're running an outdated Wi-Fi connection standard or have an extremely high-speed Internet connection, there's the possibility that the Internet connection speed is faster than what the router and Wi-Fi adapter can support. In this instance, updating the router and adapters to a faster connection speed will allow the computer to access the Internet at a faster speed compared to the older standard; however, the Wi-Fi isn't making the Internet any faster, it's just able to use more of the bandwidth that was already there.

Using Dual Band

Adding a second Ethernet adapter on a wired connection can improve network connection speeds because it creates two separate connections with dedicated bandwidth. The problem with using multiple Wi-Fi connections is that the wireless access point's bandwidth is already maxed out from just one adapter. It would be like using a Y-adapter for a comparable wired connection: the speed is capped at the network connection point. One way to work around the single-connection limitation is to use a dual-band adapter to broadcast on both the 2.4-GHz and 5.0-GHz standards, which creates two separate connections. However, the dual-band wireless standards run on a singular router and Wi-Fi adapter, negating the need for a second adapter on the computer.

When Using Two Adapters

When you run a computer with two wireless adapters, the computer will use the faster mutually shared connection standard between the adapters and the router to connect to the network. The secondary adapter will only be used if there is a problem with the primary one. Unlike with Wi-Fi connections, using multiple cellular network wireless adapters can improve Internet connection speed. The cellular phone towers do not max out on bandwidth over a single connection, so a device can use multiple adapters to establish and thread several connections into a single data stream.