Dan's Data has posted a review on the Topower TOP-420P4 420 watt ATX power supply
The Power Supply Unit (PSU) is far from the most expensive component in most modern PCs.Read more
Most no-brand clone PCs use the PSU that came with their case. Stock PSUs in half-decent mini-tower cases are likely to have about a 250 watt rating - not many small cases come with a 300 watt PSU as standard.