The i5-3550 is supported it's the HD2500 graphics that are not.
How are you connecting to your monitor ? DP or VGA ? Post a screenshot of the graphics section of System Information. You can also post a screenshot of About this Mac as well. Also , open up the chess app. Try to move one of the pieces and see if it works.
I know that HD2500 graphics do not have Metal support, Even HD3000 do not have metal support. Are you certain there is no dedicated graphics card installed in your Dell ?
I have an i5-3470 and the HD2500 does "work" if you boot from a Unibeast installer. You only get 7mb of Vram and no QE/CI. You can see from the following screen shots. If you have HD2500 graphics and more than 1024mb of Vram, it's possible to get that with a fake ig-platform-id that mimics HD400. It usually doesn't give you fully working integrated graphics. Provide details of how you've made it work if it is actually fully working.
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