I’ve had an emachines for like 5 years and it’s been a solid performer - had to replace the HD recently but was able to use the restore disk to put the OS back on and works great again. In general the only way they can sell these machines so cheap is to use off the shelf parts, so pretty much anything you can think of is pretty much standard.
I’ve always built my own and learned (the hard way) that the p.s. is one item worth throwing a little extra money at.
That and the graphics card, of course... ;o)