: Prebuilt manufacturers often save money by using "just enough" power supplies that lack the overhead needed for future upgrades like a new graphics card.
: If a part dies in a custom build, you only mail that specific part back. With a prebuilt, you often have to ship the entire heavy tower back to the factory. building your own computer vs buying one
Are you using a screwdriver and following a 2-hour tutorial? : Prebuilt manufacturers often save money by using