I Think the demon king would have a power level around 450 Thousand hear me out he woul've starter with around 1M power level but he gave half of his power to commandments making him 500K and since his aging and his body he would be around 250 thousand but after purgatory in those rough conditions its atleast 450K Im also gonna talk about the supreme diety i would say the supreme diety has a higher powerlevel than the demon king Since the demon king has his 10 Commandments and the supreme diety has her 4 Arkangels which one ark angel is 2 commandends which means it would be like 8 Commandments take on 10 so that means supreme diety gave less of her power to her ark angels and kept alot for herself so she would have 1 600K powerlevel is what i think and she doesn't seem to age as we have no proof
i think the demon kings power is 900,000
i acctually think this is the answer the demon kings power level is 291600,000 because if you do 540 times by itself then add the three zeros at the end this might be the answer.
and dont forget about meliodas because he is a son of the demon king and meliodasses power level is 142,000 the reason why i mention it because he was a leader of the tencommandments.
I THINK the true power lvl is like over 9000