The newest (3rd gen, Black/Plastic)PSU's are larger and may not fit in an older case, without removing the memory card reader.
The original PSU, was overpowered in the first place(380W)I've never seen it run over 270W.
The second generation, post 2007, ran at 280W. So I would not see any issues with this.
I actually have a PS3 PSU running a 65W dual core computer /w 3.5 harddrive and laptop dvd