I have Mooer 9V 2000mA power supply and pedals, such as MXR Carbon Copy requiring 26mA at 9V or EHX Pog Nano requiring 25mA at 9VDC. Is it safe to use this power supply with these pedals? Is it safe to use this power supply with these power supplies simultaneously (fx using Mooer Daisy Chain)?
If the voltage rating is correct, it is perfectly safe to use a power supply with a higher current rating than you need. The pedals will only take as much current as they actually use.
Of course an over-rated supply may be bigger, heavier, etc, which might make it less convenient to carry around, but it will work just fine.
If the supply has a voltage regulator it is safe, and store-bought power supplies usually do (and I'd guess this one does). However, some cheap power supplies (mostly ones that come with a particular piece of equipment) depend on the resistance of whatever you're plugging into it to regulate the voltage, so connecting a device with lower current draw could cause the supply to produce considerably more than 9 volts. I fried a scan converter this way once.
See also (emphasis mine):
For example, a regulated power supply is one that maintains constant output voltage or current despite variations in load current or input voltage. Conversely, the output of an unregulated power supply can change significantly when its input voltage or load current changes."
Your power supply should deliver 9v to all of your pedals. The only thing you should worry about is overloading the power supply. If the sum of all your 9v pedal's current ratings exceeds 2000 mA, then you could have a problem. It doesn't sound like you will ever have that problem. At 25 mA per pedal, you would have to try to power 80 pedals to reach 2000 mA (2 amps).
If you tried to use your 9v power supply with a pedal with a different voltage rating, that would be bad.
If you are using the same power supply (which doesn't provide several potential-separated outputs) with several pedals simultaneously, you get ground loops. It depends on the overall size of your setup and the magnetic fields in its placements whether this will or will not buy you significant levels of hum.