Neophyte PSU Wattage Question

So the spectacular documentation for my PCV-RX752 Sony Viao doesn't list the amount of watts the PSU is capable of outputting.

I took a peak inside and it doesnt say anything on the case of the PSU, either.

But, on the back of the PC, it reads:
AC INPUT
100-120V ~3.9A

Hark back to the days of high school physics--a little internet sleuthing and I was reminded of this formula:

watts=amps x volts

So, does the watt output of my PSU (3.9A x 100V) = 390 watts?

Is that right?

Thanks.

What Knewton said - but you should be able to find the real number (which is almost more useful as the one calculated from the UL label) by opening the side of the case and looking at the PSU itself.

Mike.