In addition to Xbox 360 and Xbox One controllers, it was discovered that Steam Link also supports PS3 and PS4 controllers. I decided to give my Wii U Pro controller a shot. :
RPCS3: PS3 Games on Your Deck – Deck Central
Amazon.com: arVin Mobile Game Controller for iPhone/iPad/Android/Samsung/Tablet/PC/Switch/PS3/PS4, Wireless Gamepad Joystick with Turbo/6-axis Gyro/Vibration, Play Xbox Cloud Gaming/PS Remote Play/Steam Link : Video Games
Steam for PS3 Portal 2 detailed - GameSpot
ENG/GR]How to use your ps3 controller with any pc game using steam - YouTube
Steam Deck natively recognizes the PS3 controller. Simply plug it in via USB, wait for Steam OS to recognize it, then unplug USB cable and it will work over Bluetooth without needing
SONY PLAYSTATION 3 PS3 (Fat, Slim o SuperSlim) Modificata con HARD DISK 500/1000Gb CON GIOCHI + CONTROLLER - Telaccomodo.it
How To Play PS3 Games On Steam Deck (The Easy Way)
Configuration] How to use Dualshock 3 on Windows with Steam : r/SteamController
Steam Link Review
ENG/GR]How to use your ps3 controller with any pc game using steam - YouTube
How to Use External Controllers on Steam Deck
Amazon.com: arVin Mobile Gaming Controller for iPhone/iPad/Android/Tablet/PC/Switch/PS3/PS4, Wireless Gamepad Joystick with Turbo/6-axis Gyro/Vibration, Play Xbox Cloud Gaming/PS Remote Play/Steam Link/Call of Duty : Video Games