Reddit mentions of Adapter for Gamecube Controller. Super Smash Bros Gamecube Adapter for Wii u, Pc, Switch. No Driver Need and Easy to Use. 4 Port Black Gamecube Adapter(Improved Version)

My personal setup:

• An OG nintendo gamecube controller for personal play
  
• Three cheapo gamecube controllers (see link above) for when friends come over (sorry pals, you gettin' the cheap stuff)
  
• This adapter: https://www.amazon.com/gp/product/B00SA5IJIM/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

Are you serious? Just get this one.

.... I swear I did a link when creating the thread. Sorry friend!

http://www.amazon.com/gp/product/B00SA5IJIM/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1#

I bought a Gamecube controller adapter off Amazon (link) and have it connected in "PC" mode. It registers as 4 GameCube Controller Adapter (regardless of controllers being plugged in) and it seems to work as input. The four logical controllers show up under Big Picture > Settings > Controller Settings, but in Steam, it doesn't appear to behave the same way as, say, my Wii U Pro controller. When I click the Wii U Pro controller, it shows options for preferences, identify, calibrate, and layout. However, when I click one of the GC controllers, it immediately takes me to layout, and although I can change the button assignments, the only options are "cancel" and "clear and exit". Backing out of this screen resets the button assignments, and the controller does not seem usable in my games under Manage Game > Controller Configuration (when the Wii U Pro controller is not connected, it says no controller is connected, even though the GC controllers are showing in global settings).

How can I make the GC controller usable?

As far as controllers go I think most people would be better off buying one of these three adapters:

http://www.amazon.com/Super-Smash-GameCube-Adapter-Wii-U/dp/B00L3LQ1FI

http://www.amazon.com/gp/product/B00SA5IJIM/ref=pd_lpo_sbs_dp_ss_2?pf_rd_p=1944687542&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00L3LQ1FI&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1DX7SZQ4P8M8EKATZTM7

http://www.amazon.com/Mayflash-GameCube-Controller-Adapter-nintendo-u/dp/B00RSXRLUE/ref=pd_bxgy_vg_text_y

and real Nintendo branded Gamecube controllers like these:

http://www.amazon.com/Super-Edition-GameCube-Controller-Wii-U/dp/B00L3LQ4B4/ref=pd_bxgy_vg_img_y
or
http://www.amazon.com/gp/product/B0017KIBAI/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

The reason I recommend this is because the latest development builds of Dolphin have native controller support built in. This means you can just setup the adapter to work with Dolphin and then plug in your Gamecube controllers and you're ready to go with no additional setup. The controllers auto calibrate just like on a real console and you can even unplug controllers and plug them back in during gameplay and everything will still work. It's works really awesome.

I have the KELUX adapter and it works in native mode. price is about the same as the Mayflash

With GameCube controllers?

If you don't want to buy the expensive switch controllers there are adapters.

I'm using an off-brand one from KELUX. It was cheap as hell (less than $10 iirc). Got it around the time Nintendo ones were $60+

http://www.amazon.com/Gamecube-Controller-Adapter-Wii-U-Nintendo/dp/B00SA5IJIM Here's the one.

No it’s this one: https://www.amazon.com/dp/B00SA5IJIM

Best seller on amazon, and gbatemp.net forums said it works with Nintendont.

https://www.amazon.com/gp/product/B00SA5IJIM/ref=ppx_yo_dt_b_asin_title_o07__o00_s00?ie=UTF8&psc=1 try this, this is the one i use and still works well

This adapter is actually really good quality and it's only $30. I ordered one a few weeks ago and it works fine.