XServe G5 shuts down - hardware error ? How to verify ?

Question

I experience a strange problem: From time to time (varies between weeks and days, happens more often recently) the server reboots. But not just the server, even the router that the server connects to.
First I believed in a DoS attack, but now more and more feel that it is a hardware issue.
Attached is the notification mail the server sends out. Maybe you find something strange there and can give me a hint.
I noticed two things:
The system controller ambient temperature is unusually high. Could this be the reason why the server restarts ? Are the sensors connected with cables which I may check ? But the number sounds strange; like something "out of range" - 65536/1024 = 64
Is it possible to turn off rebooting in case of temperature problems ?
However why is then the router affected as well ? I also suspect the UPS to have a malfunction. But it cannot be checked for that. Anyway, I removed the UPS and will see how it turns.
How can I check the hardware of the server ? I know that there is a diagnostic software at the system DVD... can I run this without booting from it ? Any other tools (beside Apple's own) that could be helpful to solve this issue.
Any help is appreciated.
Here is the mail:
"Reason for notification: Power"
OS version : Mac OS X Server 10.4.11 (8S169)
Processor : 1 x 2000 MHz
Memory : 1024 MB
BootROM : $0005.17f2
Serial : CK638000WD2
Memory:
Memory Slot "DIMM0/J11" : 512MB, ECC DDR SDRAM, PC3200U-30330
Memory Slot "DIMM1/J12" : 512MB, ECC DDR SDRAM, PC3200U-30330
Drives:
Drive 1 (disk0) : Normal
Network:
en0 Normal
fw0 (inactive) : Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
en0 Normal
Sensors:
CPU 1 Power : 19.33 watts
System Controller Ambient : 65535.50 C
CPU 1 Inlet : 27.00 C
System Controller Internal : 47.00 C
Behind the DIMMs : 39.00 C
CPU 1 Ambient : 33.00 C
Between the Processors : 30.00 C
PCI Slots : 33.50 C
CPU 2 Inlet : 26.50 C
DDR IO : 2.63 volts
CPU 1 Internal : 44.79 C
1.5v : 1.49 volts
3.3v Trickle : 3.28 volts
5v : 5.07 volts
CPU 1 12v : 3.55 amps
12v Trickle : 12.00 volts
1.2v : 1.18 volts
1.8v : 1.81 volts
System Bus IO VDD : 1.47 volts
CPU 1 Vcore : 1.27 volts
DDR IO Sleep : 2.63 volts
3.3v : 3.29 volts
3.3v Sleep : 3.27 volts
CPU 1 Core : 15.26 amps
5v Sleep : 5.10 volts
12v : 12.00 volts
1.2v Sleep : 1.18 volts
System Controller Vcore : 1.70 volts
1.5v Sleep : 1.52 volts
Controls:
Clock Slew :
CPU A1 : 4002 RPMs
CPU A2 : 3990 RPMs
CPU A3 : 4031 RPMs
CPU B1 : 4013 RPMs
CPU B2 : 4027 RPMs
CPU B3 : 3996 RPMs
System Controller : 5095 RPMs
PCI Slot : 3603 RPMs
Security:
Enclosure Intrusion : No
============================================================

Answer 1

When looking at a LIPS (a less-interruptable power supply; they've never truly been "uninterruptible", after all), there are two factors to consider: wattage, and reserve power. These are how much power can be supplied continuously, and how long that power can be supplied, respectively.
The local standard-issue LIPS is an APC Smart-UPS 1500 series. That unit runs an Intel Xserve server box and its few associated (core) giblets nicely; with an LCD display, USB hub, network switch.
With a USB connection to the host, this APC unit is automatically recognized by default by Mac OS X Server 10.5 Leopard Server.
Typical run-time with an outage with the 1500 watt unit is about five to maybe fifteen minutes before the shutdown is triggered. This range depending on how hard the box is running. (Yes, the upper-bound on the run-time is a little murky here. It's (also) definitely subject to the age of the battery in the LIPS.) Typical power outages at the sites where these are deployed are less than this range.
With the local preference for (unnecessary?) redundancy, it's typical to run parallel LIPS; one per box. That consistency also means fewer (different) spares need be stocked. Though with the Intel Xserve with dual power supplies configured, it's also feasible to run a pair of larger LIPS and to split them across some number of servers to gain some economy.