Best thing to do is connect the drive to system connected to the highest SATA number on the main board so if you have 4 SATA connections and they are marked as SATA 0,1,2,3 connect the drive in question to SATA 3 and have your drive with the OS connected to SATA 0 or SATA 1. If you only have two SATA connections connect the systems hard drive to SATA 0 and the drive in question to SATA 1.
The power connection is rated for any SATA type drive no matter hard drive, solid state drive, or DVD or CD ROM drive.
Only danger of connecting drive to your computer would be if the drive has a virus on it and its the type that can spread to the working system drive, but if you have an up to date antivirus running on your system you should be fine.
You will want to test the drive with CrystalDiskInfo which will tell you if the drive is healthy or not according to S.M.A.R.T data on the drive.
Other option is buy an external hard drive case empty and install the SATA drive to it and connect that way, or get a SATA /USB Dock to connect that way. But the free method is if you can connect it internal vs buying external enclosure for it.