The differences in power consumption between the Intel® SSD S3500 and the Intel® SSD 320 is primarily due to design considerations based on the target market for each drive.
The S3500 is designed for the Data Center market where power consumption is secondary goal. Response time, reliability, data integrity and endurance are the primary design goals for this market. This drive does not support Device Initiated Power Management since that would reduce response time.
The 320 series is designed for the Consumer market. Power consumption is a primary goal for this market since it’s anticipated that this product would find their way into form factors (laptops/tablets etc.) where battery life is very important.
The measurement methods do make a difference. We use a more strenuous workload when measuring power consumption on the S3500 since that is representative of the anticipated real world usage of the product.
I hope this information is helpful for you.