Long time ago, power supplies delivered power mostly on the 5.5 and 3.5v rails where the then gen processors needed power.
Today, power is drawn mostly from +12v.
Your cpu may draw 100w, and the GTX750ti slot power may be 75w.
If you look at the data plate above, you can see that the max 12v amps is 20a.
Translated to watts, that is 20a x 12v or 240w
Nowhere near the 700w .
But, a power draw of 175w out of 240w may be ok if the psu is sound.
What to do??
You could abandon all thoughts of gaming.
Or, you could give it a try with not much to lose if the psu overloads and damages parts.
Since the psu has apparently been working ok up to now, there is some confidence.
For safety, do not leave it unattended.
What is your budget, and where might you shop?
Does your motherboard have a legacy bios(as compared to uefi)
Modern motherboards use uefi.
The issue is that some modern graphics cards like a 30w GT1030 will need a uefi bios to get detected.
The nvidia 700 series was the transition point between legacy and uefi.
Some cards could handle both, and some could not be detected on a legacy bios.
If you are buying a card, do so from a seller which can accept a return.
It might be a good idea to make plans for a new pc.