Let's see, 1) I would never replace an NVMe M.2 SSD with a SATA drive. The NVMe speed is roughly 7x faster than a SATA SSD. And yes a 2.5" drive would block the M.2 slot but again You would not want to use a SATA 2.5" SSD instead of an M.2 NVMe SSD. 2) The 5510 does not support M.2 SATA SSD so you have to replace an NVMe with an NVMe. 3) The 1TB drive is the largest that Dell has tested the 5510 with but you can go as large as 4TB. And there is no point going with a Gen4 M.2 drive, though it is backward compatible, as they may be more expensive in many cases than a Gen 3 M.2 SSD. As an example the Crucial site here lists a number of compatible SSD up to 4TB in storage space. 4) There are no voltage variations in M.2 drives. A standard M.2 NVMe SSD will work in your system. I hope this helps out.
hello every one my sister have dell latitude 5510 with m.2 micron 2300 Nvme 256GB, it's not enough storage for her and I want to buy her new SSD and I have some questions, 1. there is m.2 slot in the laptop but in the dell website I saw there is another slot for 2.5 Sata ssd I search in the internet and it was said that you can't add another ssd in the 2.5 Sata slot because he blocks the m.2 slot so you need to choose only one of them, is it true? if I want to buy 2.5 Sata ssd I need to throw away the m.2 one? 2.  if I want to throw away the m.2 micron 2300 Nvme 256GB and replace him with different m.2,the m.2 need to be also Nvme or I can replace him with m.2 sata?3. here at dell website it said that when the form factor is One M.2 2280 solid-state drive then the CAPACITY is Upto 1TB does it means that if I buy 2TB ssd it won't work?also it said that it up to 32 Gbps so if I buy ssd that is more than 32Gbps it also wont work in the laptop? 4. is there voltage that I need to look up to when I search for ssd to buy? Are there voltages where it will not work ?  
upgrade ssd dell latitude 5510