While the PlayStation 3 is able to connect with almost any controller, so long as that controller has a USB connection, the PlayStation 2 DualShock2 controllers do not fall into this category, because they were designed to interface with the PS2's ports. Should you want to use a PS2 controller on your PS3, whether this is because you want your PS2 games to run more smoothly or because you'd rather not have to worry about a wireless controller's battery supply, you will have to use a specially designed PS2 to PS3 adapter.
Using PS2 Controllers with the PS3
Ensure that the adapter you have chosen is compatible with the games you want to play.
Insert the end of your DualShock2's controller cord into the larger end of the adapter.
Connect the other end of the adapter, the end with the USB lead, into your PS3.
Start up your PS3 and begin playing.
As you choose your adapter, keep in mind that, while most will work across a broad spectrum of PS2 games, others are not compatible with Guitar Hero or DDR peripherals made for the PS2, while some are intended specifically to be compatible with those peripherals. The product information provided by the company selling each adapter, user reviews, like those that can be found on Amazon.com, and reviews on technology blogs are all good sources to find information on which games these adapters will work. When using an adapter, the DualShock2's “Analog” button is analogous to the DualShock3's PS button, allowing you to reset the console, turn the controller on or off, and toggle analog stick support for original PlayStation games. As an added bonus, many of these adapters can also be used in order to let you use your DualShock2 controllers on your PC.
You should be aware that certain features simply do not through adapters. When using PS2 controllers for PS3 games, you will be unable to play parts of those games that require Sixaxis support. Force feedback, which causes controllers to “rumble,” is also not supported in PS2 or PS3 games when you are using an adapter.