Some computers don't supply the SL-1 with enough juice. That's basically the reason...

well, that is weird, but, to be safe i'd use the 9volt adapter anyway.
i mainly use mine b/c i dont always have my computer on when im mixing, sometimes i just play straight vinyl.
do you get a lot of dropouts with your box? if it performs as it's supposed to plugged in to the adapter, i wouldnt worry about it.
Josh

...but my computer must provide it enuff juice because it worked with someone else's box. The guys box I was using was a celebrity's, so I'm wondering if rane provided him with a "juiced up" box that is all...

Hmm...Did you plug it into the same USB port?

The boxes will vary slightly from one manufacturing run to the next. Your laptop must be right on the borderline for supplying enough power. Personally I always use the power adaptor anyway even though it runs fine on all my computers. It makes setting up easier because you don't have to plug in your laptop for the thrus to work.

It is your laptop. I have seen my laptop sometimes powering up the box and sometimes not. So its not consistent. As nobs said, the power on the USB of your laptop might be on the borderline.

Is it possible that if your computer is not providing enough power to the box that maybe after a few minutes of running the program that the computer will lock up including the program locking up and you must completely reboot.

I wouldn't think so. I just think you would get the interface disconnected message.

What is your CPU like when this happens?