8-pin has the same number of power pins, but it has two more ground pins than a 6-pin PCIe power connector. The adapter works because the extra two pins can be grounded, but your current carrying capacity is reduced in comparison.
The external power for these powerful graphics cards comes from the 6-pin and 8-pin PCI-Express power connectors from the power supply. Here I am going to discuss the graphics card power requirements and its PCI-E power connectors.
Every modern-day graphics card comes with a PCI Express x16 connector that goes in the PCI Express x16 slot of your motherboard. PCI Express x16 connector connects your graphics to the motherboard and is the only interface through which communication happens.
Possible solution: Get a 4 Pin Molex to 6 Pin PCI-Express PCIE and a dual 6 pin to 8 pin PCIE so you can pull some from the molex connector as well. You are a very brave soul. I would be reluctant with a 400w PSU. It *might* work but you have absolutely no headroom for additional draw or overclocking if you do.
PCIe in the CPUs is an interface standard connecting many superfast components for high-speed data transmission using the power source from the motherboard. You can find PCIe slots in every computer or motherboard that enable users to connect GPUs, SSDs, and raid cards.
The 6-pin graphics connector is usually common in lower and mid-range graphics units. As the name says, the connectors have six-pin connecting slots with a 4.2 mm pitch. These GPU connectors can directly draw up to 75 watts from an external power source. The power even comes bypassing the motherboard.
An 8-pin GPU cable is a power connector common in most high-end graphics. These connectors usually have a 4.2 mm pitch that can seamlessly offer a power supply of 150 watts. If you connect a graphics card with an 8-pin connector, the maximum power supply you can draw is 225 watts.
The 12-pin GPU cable is the most trending development from the NVIDIA graphics company. The connectors in these cables come with a 3.0 mm pitch. This implies that its real physical dimension is the same as an 8-pin connector, and it also doesn’t occupy much internal space for the airflow.
When gaming enthusiasts build a PC, they come across any compatibility issues. In the case of connecting components, the same thing happens as well. You can find power connectors that are not compatible with the motherboard or other hardware in the computer. Undoubtedly computers around the globe get manufactured by different brands and engineers.
If your PSU is too old and you lack connectors, upgrading your PSU in such cases would be wise. It is because; your older PSU had an older configuration. It was designed to meet the power requirements of PSUs in the past. However, the recent power requirement scenarios are entirely different.
The GPU power connector is commonly known as PCI express cables or PEG cables. The PCIe express cables are also termed to describe 6-pin connectors. However, the power supply connectors in the motherboard are known as PCIe connectors. Every computer/PSU has PCIe x2, 4, 8, and 16 slots.
The adapter works because the extra two pins can be grounded, but your current carrying capacity is reduced in comparison. If a connection is loose, you could start a fire under heavy load.
Basically 6 & 8pins are one and the same and can of course carry the same amount of power.
I use dual 6 pin input to single 8 pin output for years now, no issues. I did find one adaptor that was not fully wired.
I use an adapter myself but my 12v rail can supply enough to allow me to use the 6+2 pin adapter - been using it for 8 months with no issue but it is a quality OEM supply. Some supplies, particularly cheap ones won't be safe supplying 150w through that single rail with an adapter on it.
i would just save some $ and get a proper wattage psu so u dont have to worry about this again in the future. 550-650w will do fine and last a cpl of builds if you upgrade down the road.