Advice needed for connecting an old PSU to a 6-pin PCIe connector

[Ady2009]

I am trying to fit a GTX 1650 into an old PC which has got a 350W power supply. I deliberately picked this graphics card as it says it only needs a 300W PSU to work and so it seemed to be the most economical solution for an old PC. There is no 6-pin connector coming out of the PSU but I did dig out a 2 - molex to 6-pin PCIe connector which I though would work but have hit a problem... The PSU has only got 1 molex connector and so I am stuck!

The outputs from the PSU are:
1 x 24-pin ATX connector
1 x 4-pin ATX connector
1 x output leading to 1 molex connector
1 x output leading to 2 SATA power connectors
1 x output leading to 2 SATA power connectors

My understanding from the spec below is that the PSU has got 2 x 12V rails but I just do not understand how the power output from the 2 rails is split between all these connectors. Is anyone able to help clarify?

+3.3V (20A) and +5V (20A) = 130W max
+12V1 (17A) and +12V2 (17A) = 324W
-12V (0.8A) = 9.6W
+5Vsb (2.5A) = 12.5W

Total of 350W apparently!

I just don't understand what outputs come from the +12V1 and +12V2 rails. I understand that I need to split the load between both rails but am not sure how - ie, how the molex or sata power connectors would be split between the rails. Would a single molex to 6-pin PCIe connector work instead?

 

[Ady2009]

I should have clarified that it is a Seasonic SS-350ET PSU.

 

[Uriel]

A stock GTX 1650 is rated at 75w - but yours has a 6 pin connector? Not all do. OC versions may draw more.

The GTX 1650 Super is rated at 100w and usually has a 6 pin connector.

In either case the PCIe slot can provide up to 75w. Not a huge additional power requirement from the cable. I would be tempted to use an adaptor in this case. You can get SATA ones as well as molex.

 

[Quartz]

I am trying to fit a GTX 1650 into an old PC which has got a 350W power supply.

I am no expert, but I've been messing about with PCs for nearly 40 years and one lesson I've learned is to not skimp on the PSU.

My understanding from the spec below is that the PSU has got 2 x 12V rails but I just do not understand how the power output from the 2 rails is split between all these connectors. Is anyone able to help clarify?

You should check the manual (Google has failed me) or contact Seasonic but the likely configuration is that one 12V rail goes to the motherboard and the other goes to the Molex and SATA connectors. Molex is specced to carry up to 130W on the 12V line with good enough cables (and SATA to carry up to 54W). So in theory using just the Molex should work but without speaking to Seasonic I wouldn't trust it. The cables need to be specced to take the power (remember they need to cope with power spikes) and you don't want them overheating and failing. Or worse, catching fire. Another failure mode is that if the GPU cannot draw sufficient power from the cable it will try to draw it from the motherboard and that could be expensive, causing the slot to fail.

Would a single molex to 6-pin PCIe connector work instead?

Theoretically. Molex can deliver up to 130W. Your double connector may work with just one Molex plugged in. Speak to Seasonic.