As for the preparedness of a nation to handle a cashless economy during a time of war, wouldn't a electronic ledger be must safer and reliable than if the government say just started printing more money leading to inflation problems. This has happens numerous times throughout times of history during war and could be avoided with a cashless economy.
No. Aside from the added vulnerability of the infrastructure needed to maintain and interact with an electronic ledger, such a system either still allows a government to issue new tokens (and thus has no effect on the issue you raise) or requires blunter, higher overhead means at serving the same national functions that wartime money printing serves, which means either (or both) more internal disruption or greater probability of losing the war.
During a war power plants will get bombed. Network and power cables will get bombed. Roads, railroads and bridges will get bombed, so power plants wouldn't even get fuel.