If the meter is plugged into the UPS, then the UPS has nothing to do with the power flowing into the meter. Power is “pulled” not “pushed” to devices in that a device supplying power can limit the amount of power provided, but can’t increase it beyond what the devices request.

Just like with plumbing. The water company can’t force your faucets to open and use more water. Now they could increase pressure and break pipes, similarly the UPS could provide the wrong voltage and short or burn out wires or devices causing them to draw more, but that is unlikely to be the issue here. As long as voltage is constant, amperage (the other component in wattage) is pulled, not pushed.

What you’re seeing in the input load, if it matches what is flowing out of the meter, is some device requesting more power and thus more power flowing into the UPS to be passed to those devices, not the UPS forcing something to use power which isn’t possible as explained above, or the UPS itself using power because the meter has no connection to what power is being used by the UPS, only things plugged into the meter.

So, there must be something else using the power. Likely the devices, even if they aren’t really doing anything you consider significant, are doing something. Probably maintenance, checking for updates, the monitoring proceses requesting information from the devices since the TrueNAS server is on that end, etc. You’d need to put a meter on each device to determine what is drawing the power specifically.

Also, does the power meter only display power used by devices plugged into it, or does it also display it’s own power usage? Could be that the plug itself is using WiFi or something to communicate with external services to log that data. But that would be quick bursts.

Also, without putting a meter on each device, this is probably cumulative. For example, if the NAS is requesing info for monitoring the network, that would spin up the processors on the RPi an cause the switch to draw more power as it transmits that information across the network. Again, this should only be small bursts, but it’s also possible the devices are not sleeping properly after whatever process wakes them so they continue to run their processors at higher amperage for some time. Tweaking power profiles can help with something like tuned on Linux or similar to make things sleep more agressively. With the drawback that they take some amount of time to spin back up when needed.

Sounds unrelated to the UPS if you’re measuring that load on the output. I wouldn’t worry about it, computer/server loads fluctuate constantly and that’s normal.

The UPS needs some power to keep its batteries full. Could be that it’s triggering off some threshold to do a charge cycle instead of just running a constant trickle. I’ve noticed that my laptop and phone charge that way, for example.

It’s weird to do this daily, but it’s possible that the UPS is doing a self test, which would drain the battery a little and the load is from charging it back up.

So what is the TrueNAS server doing at this time? Have you checked the logs?

I would image it might be some backup, snapshotting or optimization.

What’s in the UPS log?

UPS devices normally uses wall (input) power, and switches to battery when input voltage is out of the target thresholds. So, input.load should represent the percentage of current wall power (in VA) relative to UPS’s max rated input power (VA). If your devices uses more power, input power from wall should increase as well.

If it’s peaking in certain times, it could be due some scheduled job temporarily increase CPU frequency, or automated tasks like file system snapshot might power-up/spin drives longer than regular usage.