I am powering one Mikrotik from another via POE, I have 2 power supplies which would be the best for powering the master Mikrotik
PSU 1 is 24v and 0.8amp
PSU 2 is 12v and 1amp
Thanks 
Depends on voltage requirements of both units. If both jnits accept it, go with higher voltage as it means lower current with lower loss on cables. Be sure to use power adapter with adequate current rating: add up rated power consumption of individual units and make sure power adapter rating is matching (or slightly above) that.
Example: if both units accept 24V, use that. If rated power consumption of units is 13W and 10W, then combined rated power consumption is 23W. Divide that with PSU voltage (24V in this example) and calculate combined amperage: around 0.96A … so the PSU should be rated at 24V and at least 1A (better yet go with around 20% higher, i.e. 1.2A).
Another thing to care about is potential limitation of PoE out max current - check your unit’s specs.
[edit] fixed power calculation
Thanks