Is 300W Power Supply enough??

A customer who bought his PC elsewhere, is having problems with it restarting itself. It seems to happen only when connected to the internet through his ISDN connection. Apparently the ISDN connection is dropping out, even when the computer doesn't do a complete restart.

I'm seriously suspecting the power supply. It's marked as a 300W, but the customer has a LOT of devices in the system, and I'm wondering if 300W is enough juice. Here's what I remember of the system specs:

Microstar Mainboard
Pentium 4 CPU (I think 1.7GHz)
Radeon AGP Video
NetJet ISDN Modem (PCI)
Realtek 10/100 NIC
Pixel View TV Tuner Card
ESS 16 bit sound card
Pioneer DVD Burner
DVD Player
40GB Western Digital 7200RPM HDD

So what do you think?? Is 300 watts enough?

Thanks in advance for all input.

Although I'm pretty sure it's ok I would check another one. Then maybe I would check the memory as well.

wattage isn't the ultimate measurement of power supplies. who makes the supply? How heavy is it? a high quality 250watt supply from a good manufacture like antec, pc power and cooling, or enermax will be better than a generic 300watt supply. test the system with a high quality 300-400 watt supply and see what happens. also check all the voltages in the bios or with a voltmeter and make sure all are within normal ranges.

Agree with all above posters...usual PC in fact consumes just only something about 100-150Wt (monitor is not count here). But generic 300Wt PSU may be in fact just as powerful, as ... 200Wt PSU from one of the good brand manufacturers like mentioned above. Besides that, cheap generic PSUs usually doesn't have EMF (ElectroMagnetic Filters) soldered... <img border="0" title="" alt="[Eek!]" src="eek.gif" />