The short circuit current can easily reach several 100amps for most larger power transformers.
Guessing from the secondary coil, the continous current is probably 20-50A, so 200-500VA.
Did you wind the secondary yourself?
You can easily test the continous power capability by loading the transformer and measuring its temperature. When it rises by more than 40°C, it is at its rated power. But do it slowly, because it can take hours until the temperature has settled.
This is my heavy duty power supply: HP6260V: 0-10V, 0-100A.
There is another row of two capactitors below the three ones. Under the control pcb is the heatsink with a large 120mm fan.
The grey part of the transformer is the primary winding, the white/brown part the secondary. The secondary winding uses a large copper strip. Its resistance is less than 1mOhm.
Only the transformer weights around 23kg. The small transformer on top is a microwave oven transformer.
I estimated a short circuit current of over 2kA for this beast, drawing 300A on the primary side and dissipating 15kW.