Helping people with computers... one answer at a time.
Replacing a power supply is reasonable common solution to some problems. Making sure you have the right wattage power supply is important. And bigger doesn't hurt.
I want to upgrade my current case that has a 300W PSU to a nicer looking case, but it has a 520W PSU. Is it ok and how does the "W" difference influence PC operation?
It's quite all right, and if things were working well before, you probably won't notice a difference.
There, now that I've answered the question, let's look at why, and just what that "W" means. I get questions on this topic frequently.
The "W" stands for "Watts", which is a measure of electrical power. A power supply with a higher wattage rating is capable of delivering more power to your computer.
That's more electrical power. It won't make your computer run any faster or give your more "computational" power - this is simply about electricity.
A new power supply is typically called for in one of two situations:
Your existing power supply is failing. Either it has failed completely or it's "slowly" failing and no longer able to produce the power your computer requires. As it fails, unexplained crashes usually become more frequent.
You've added hardware in the form of add-in boards, memory expansions, additional hard drives, or other devices that draw power from your computer, and you've exceeded the previous power supply's capacity. This, too, can behave like a failing power supply.
In either case, the solution is a replacement power supply. In the first case, a power supply with the same rating as your old one will do; in the second case, you'll need one with higher wattage.
I typically recommend replacing with a higher wattage supply, anyway, since it harms nothing to do so.
I've heard a concern that a high-wattage power supply can somehow "force" the power onto the computer, causing overheating and burnout. Nothing could be further from the truth. A power supply supplies power in response to need; it doesn't push power anywhere. If your computer only needs 100 watts, then a 500 watt power supply will only supply 100 watts. Why have a 500 watt power supply? For "peak" usage (sometimes hardware will require sudden "bursts" of power, such as at start up or under high load) and for future expansion.
It's better to have too much power than too little.
Two important aspects of power supplies:
Get the right size. By this I mean physical size -- there are several standard sizes out there, and they are not interchangeable.
Make sure the machine is well ventilated. A higher capacity power supply will run warmer, particularly if it's providing more power. Make sure that its fan and any additional fans in your machine are working properly and that the airflow path is unobstructed. Overheating due to blocked airflow is perhaps the most common cause of PC equipment failure.
Oh, and if you have a laptop - you're out of luck. Laptops come with the batteries and power supplies that they come with. There's no real way to "upgrade" their power capacity.