How Does Proof-of-Stake (PoS) Differ from Proof-of-Work (PoW) in Resisting a 51% Attack?

PoW requires controlling 51% of the total computational power (hash rate), which demands significant hardware investment and electricity costs. PoS requires controlling 51% of the total staked cryptocurrency supply.

While a PoS attack is cheaper in terms of energy, it requires a massive capital outlay to acquire the coins. PoS also often includes 'slashing' mechanisms to punish malicious validators, increasing the financial risk for an attacker.