This system has to be 3-4 years old, why are you asking this now?
Many systems from that time came with 250Watt power supplies and they were sufficient, more would be better, but if it has run for 3-4 years it probably was enough.
If you needed to replace it you probably want to get a 350-400 Watt PSU, but unless you are having problems you don't benefit changing out a power supply on such an old system.
My present PSU is 250Watts - Is this enough power for my system described below?
Motherboard without onboard devices
2 x Fans (including PSU fans)
Memory (512 SDRAM)
1 x Graphic Card
1 x PCI Sound
1 x PCI Network Card
2 x HDD
1 x CDRW
1 x DVD
1 x Floppy
1 x USB devices
1 x Keyboard
1 x Mouse
1 x PCI Modem
CPU: Intel P3 @ 651GHz
Windows XP Pro SP2
Tks
Poltonis

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