do u think its possible to series 2 usb 2.0 port so that u can achieve 10VDC max as each port delivers 5VDC? and would u still get a max. of 500ma in current? Reason why i am asking this is because i have a amplified speaker that requires 9VDC @ 400ma and it have to plug in the wall socket to operate. The speakers play very good. And i need them to take with my laptop on the go without have to be near a wall socket to plug in the speakers. I was wondering if i could power it from the laptop usb ports instead. getting the 10VDC by adding two ports output power then using a resistor to cut down the volts from 10VDC to 9VDC and also the current down to 400ma as i have done some research on the net and they say the usb 2.0 port delivers a max. of 500ma. So is this possible anyone?

 

No.

The USB spec calls for 5v @ 500mA output. Many laptops don't output the full 500mA.

Even if you COULD get it to work, you would just drain your laptop battery that much faster.

Headphones sound good, don't require batteries, and you won't annoy others that may be within earshot.

 

The USB ports are powered from the same 5V supply in the computer.

Trying to series them would actually put a direct short across the 5V power.

There are lots of battery-powered speakers about for use with laptops, I'd look for some of those.

(I have these: http://uk.europe.creative.com/products/product.asp?category=4&subcategory=29&product=13602 )