Removing resistor in Source Transformation method
The power supplied by the 250V source is the product of its voltage (250V) and current. The current through it can be found by superposition.
With current source open, you do not care about 10\$\Omega\$ resistor and you can remove it. Calculate the current though the voltage source, call it \$I_1\$.
With voltage source shorted 125\$\Omega\$ doesn't matter so remove it, calculate the current though the voltage source again, call it \$I_2\$.
Total current should be \$I_1+I_2\$, and power supplied by voltage source is \$250(I_1+I_2)\$.
Follow a similar analysis for the current source.