Please help me what the point I had wrong
The sources provide \$\small (P=VI)\$:

\$\small 10A: 296.43\times 10=2946.3\:W\$

\$\small 50V: 50\times 3.57=178.5\:W\$

\$\small 5A: 128.57\times 5=643.75\:W\$

Total = \$\small 3786.55\:W\$

The resistors dissipate \$\small (P=I^2R)\$:

\$\small 5\Omega : 3.57^2\times 5=63.72\:W\$

\$\small (10+5)\Omega: 8.57^2\times 15=1101.67\:W\$

\$\small 15\Omega: 6.43^2\times 15=620.17\:W\$

\$\small 20\Omega: 10^2\times 20=2000\:W\$

Total = \$\small 3786.55\:W\$