Could it be the UPS?

It looks like our aging UPS is failing, and when doing so, sometimes cuts the power to all the devices is serves. Indecently, this exactly is what UPS is supposed to prevent, but for its defense one is not supposed to run a UPS without replacing its rechargeable battery for... 10 years. We decommissioned this aging UPS, which might have been the cause for the recent periods downtime.

Machine off

For the second time in the last couple of months, the server has been down, and when looking at the problem we found that the machine was just turned off. It wasn't manually turned off by mistake, and we couldn't find anything useful in the logs. Also the temperature in the rack is not exceptionally high, which unfortunately may point to failing hardware.