Standby Power Consumption
Even when you turn your PC off, it continues consuming energy. In order to totally shut it down, you have to either pull the power cord or switch off the PSU using its power switch.
The power a PSU needs in standby is called vampire or phantom power, since it's consumed without the power supply doing anything. This power is mostly lost on the PSU's 5VSB circuit. That's why all modern units are equipped with standby PWM controllers (and/or specially-designed PFC controllers) able to minimize phantom power requirements.
In 2010, the European Union released a guideline on Energy Related Products (ErP Lot 6), which states that every electronic device should have below 1W power consumption in standby mode. In 2013, this limit was further reduced to 0.5W. The same year, the EU also released the ErP Lot 3 guideline for computers and servers, mandating that all PSUs should consume less than 5W when the load is equal or less than 2.75W at 5VSB with universal power input (100V~240V).
In our experience thus far, vampire power is lower with 115V input than 230V. It's the opposite for our 5VSB efficiency results, meaning that with 115V input, the 5VSB rail's efficiency is higher. Usually, higher voltage levels enable lower energy losses, since fewer amps are needed at 230V compared to 115V. And as current drops, energy losses do as well (P= I2 x R).
MORE: How To Choose A PSU