Both Devops and Site Reliability Engineering (SRE) aims at reliable and efficient but there distinct focuses between both.
Devops is a practice that focuses on collaboration between development and operations with high speed delivery & error free
SRE mainly focuses on reliability & availability of systems and services. It used error budgets to maintain a balance between new releases and existing systems. SRE relies heavily on metrics, monitoring and alerting to maintain SLOs and SLIs