Modern non-military jet engines are designed with high pressure ratios around 50-60 to get good subsonic cruise efficiency.

For a supersonic jet, a lot of the compression is done by the intake, so the compression in the engine must be much lower, around 10-20. This is why off the shelf engines don't work very well for supersonic.

The concorde used a pressure ratio 11.3 from the engine, but combined with the intake it was 82 when at cruise. This actually made it very efficient at 43%. During taxi and climb-out however, the low pressure ratio made it a real gas guzzler.

https://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593