Andoven, The Error Code: 2900:XXXX is  historical referring to the past system errors. It is usually good to clear the hardware logs before running system diagnostics. Did your firmware update include firmware on the Power supply?  I assume both your PSU status lights are both green.  If installed, clear the logs in OMSA and then reseat the power supply on the right (PSU 2) and see what OMSA reports. Let us know the status of the PSU 2 within OMSA and the current firmware version.
My VMware ESXi host recently took itself offline. When I was looking for the root cause, I ran a diagnostic test on my PE R710, and the following error was generated: Error code: 2900:0221.Msg: IPMI - : power supply: Power supply sensor (Status) Failure detected "PS 2"  The given error code and message can be used by Technical Support to help diagnose the problem.Do you want to continue testing? -- end of error message -- I saw a post online about updating the BIOS and firmware, which I did. We are now running BIOS version 6.4.0. I reran the test with the same results. Any ideas on what I can do to fix this problem? If the problem is indeed a failing power supply or a sensor on a power supply, how do I tell which one is bad? The lights on both power supplies look the same from the back of the server. This unit is no longer under warranty.  
IPMI error code 2900:0221 Power supply failure detected on PE R710