Side-by-side specifications of the Synology RS408 and RS408RP, from official datasheets. Differences are highlighted.
| RS408 | RS408RP | |
| CPU | 800 MHz | 800 MHz |
| Cores / threads | — | — |
| RAM (base) | 512 MB | 512 MB |
| RAM (max) | — | 512 MB |
| Drive bays | 4 | 4 |
| Expandable to | — | — |
| M.2 slots | 0 | 0 |
| Network | 2x Gigabit | 2x Gigabit |
| 10GbE | no | no |
| Max raw capacity | 4 TB | 4 TB |
| Hot-swap | yes | yes |
| Form factor | 1U rackmount | 1U rackmount |
| Released | 2008 | 2008 |
Pick the RS408RP only if you need the dual power supplies for redundancy; otherwise the RS408 is the better value. For the decision you asked about, both are effectively the same on core hardware: same CPU class, same RAM ceiling, same bay count/expansion, and no built-in 10GbE or M.2 on either. In short, buy the RS408 unless redundant power is a must-have.