You can buy up to 5 years ProSupport.
Expired Warranty Hardware Support: Even after your warranty has expired, Dell can repair systems with a one-time hardware repair service. Find diagnostics tools, contact a service expert, or find one-time repair options here
General support is 5 years after end-of-sales for both servers and workstations.
First normal care packs (up to 3 years), then Post Warranty Allows extending an 'expiring' product warranty or an 'expiring' registered HP Care Pack service by 1 year or 2 years. So 4-5 years in total.