I am running rpi4 using original 3a power supply with SDD powered off the RPI with no power problems. You just need to do the math on all the peripherals you connect to ensure your external devices do not draw more than 1.2 A
Power Supply - Raspberry Pi Documentation.
After you do the math, you may be ok, if not you can always go with a powered USB hub.
In my case, sata ssd 700mA + USB2sata adapter 100 mA + Insteon PLM 0mA + Argon One Fan 100 mA
Total = 900 mA