How much power is delivered by a voltage of 13.8 volts DC and a current of 10 amperes?
Why Power in a DC circuit is the product of voltage and current, P = E x I. Here 13.8 volts times 10 amperes gives 138 watts. This is the basic power formula from the Ohm's law family, and it's worth memorizing alongside P = I squared x R and P = E squared / R.
Watch out The 23.8 watt choice comes from adding the two numbers and 3.8 from subtracting them; power is a product, not a sum or difference. The 0.7 watt figure is roughly a division of the two, which would give resistance-like or current-like results, not watts.
Volts times amps equals watts. 13.8 V at 10 A is the classic ham power supply: 138 W.