What Is the Primary Difference in Security Model between PoW and Delegated Proof-of-Stake (DPoS)?

The primary difference in security models is the method of validator selection and the cost of attack. PoW uses competitive energy expenditure (hash rate) to secure the chain, making the attack cost the capital and energy to acquire 51% of the hash rate.

DPoS uses a voting system where token holders elect a limited number of delegates (validators) to secure the chain. The attack cost is the capital required to acquire enough tokens to elect a malicious majority of delegates, which is a financial cost rather than an energy cost.