Your G5 15 5500 came with DDR4-3200 RAM. Your Inspiron 5579 came with DDR4-2400 RAM, which is a lower frequency (slower).  You could put the G5's RAM in the Inspiron and it may work. Ideally, you should remove the RAM that is currently in the Inspiron, as mixing RAM brands or speeds is more likely to encounter issues. If the DDR4-3200 works in the Inspiron, it will automatically underclock and run at 2400 frequency. Whenever handling RAM and touching internal components, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. I know many people do such work without this, but it's a cheap and sensible precaution.
Hi I have a "Dell G5 15 5500" and an "Inspiron 5579", I want Upgrade both laptops RAMs, Can I use G5-5500 RAM (speed 3200) in Inspiron 5579 (speed 2400)? I will appreciate to help in this regards? E.Fatemizadeh  
Ram Speed Compatibility