Mac Pro power supply replacement?

We're on our yacht in Hobart, Tasmania. No access to Apple Store.

Re: Mac Pro 2006, how do I assess whether the power supply is failing?

I ask because we have experienced several times over the past couple of years the following issue. Typically in the morning I see the Mac Pro has shut down and will not startup. I go through the SMC reset procedure as per Article: HT1806. The straight forward "press the SMC Reset button" never works. Sometimes just pulling the power cord for a few minutes works. Yesterday was one of the "hard cases". None of the usual voodoo worked, so I left the Mac Pro for about 6 hours with power and all cables disconnected.

When I reconnected power the MP began a familiar 17 second cycle, both sets of Memory Riser Card Diagnostic LEDs illuminate for about 3 seconds, fans start, shutdown (repeat).

Pressing down the SMC RST button stops this loop, but still cannot startup.

Yesterday I pulled the top memory riser, left MP off for 30 minutes then when I reconnected power I could startup successfully. Shutdown, reinsert top rise, restart success.

I called Apple support, authorized a case. The tech went off to consult for 10 minutes or so, then came back and said "we think your power supply is probably stuffed".

To obtain a replacement supply here in Hobart is going to be difficult and expensive. So any advice on how to improve our assessment of the true source of this problem would be much appreciated.

The famous and helpful "Hatter" once suggested to another troubled Mac Pro owner to "leave the computer disconnected from power overnight". My experience is that the longer time disconnected is related to success, but I do not understand why. Why is overnight helpful?

PS - I've not done the following procedure yet, and because it is from the 2008 Mac Pro service manual it may not apply to the 2006 exactly as written. I'm including this info for the benefit of searchers who come along in the future:

Power Supply Verification

To power on, the computer’s logic board requires “trickle” power. If the system fails to power on, first reset the SMC as described in this chapter. If the computer still doesn’t power on, follow the procedure outlined below to determine whether the issue is related to the power supply.

Verify trickle power

Diagnostic LED 2 indicates the presence of trickle power required by the logic board to begin the startup process.

LED 2 should be yellow when the DIAG_ LED button is pressed, indicating that trickle voltage is present.

Verify Power Supply Is Providing Power

Diagnostic LED 8 indicates that the main power is OK and within regulation. Plug in AC power cord, and press the power-on button on the front panel.

LED 8 should be green when the DIAG_ LED button is pressed, indicating that the main power is OK and within regulation.

If diagnostic LED 5 and LED 6 are both solidly illuminated at power up, improperly seated power supply cables could be one cause of this behavior. Check all power supply cable connections to ensure they are properly seated.

PSS - I have recently replaced the PRAM battery.