You can get a sata to 8pin adapter on Ebay for a couple of quid. ATM the 1660 or 1660ti give such a boost in performance over the 1060 it really is a no brainer, and it will last you many years longer.
As for PSU I always have a spare sitting in my cupboard any way as they are the most likely to fail item on any PC and they are dirt cheap to buy.
As to the 1050ti, pointless card. Only £40 quid cheaper than the 1660, yet only gives about the same performance as a GTX960.
Just because you can buy an adapter somewhere, doesn't make it a good idea. They made and sold USB extension cables from the day USB was introduced, yet such cables were explicitly forbidden by the original USB spec.
As I already explained above, the 8-pin connector itself is only part of the issue. By spec, any card that has such a connector can draw more than the 150W which the PCIe slot and a 6-pin connector can provide. Think about it: There's no way a company would put an 8-pin connector on their cards, thereby limiting the potential places it can be used and thus limiting sales, if it weren't necessary. If it were within spec, they'd use a 6-pin connector because it will work with all the 6-pin setups
and all the 8-pin setups (given the 6+2 type connectors). Otherwise, the card manufacturer has to include an adapter, which still assumes there are two 6-pin connectors available, or force you to buy one before you can use their card. They'd be limiting their own sales for no good reason.
Not only that, if you use a SATA adapter, you (potentially) still have the current being pulled through one lead back to the PSU - only now, you're using the SATA connector that may also power all your drives. Probably not good. That single lead is conducting at least 6.2A, and there are mechanical crimps, mating pins etc to add resistance and points of failure. GPUs tend to draw more than most other components in PCs for gaming, and that's not really the place where you want a lot of questionable ideas hooked together.
By spec, if a card has an 8-pin connector (regardless of what you try to 'adapt' it to) then the card can draw up to 225W (75 for the PCIe slot + 150 for the 8-pin). Although it's not required to draw that, if it has an 8-pin connector, that means it draws more than 150W. The OP's PSU is fine with a card that draws 75W, even 150W almost certainly. But the cards you're talking about have 8-pin connectors, and that means over 150W, up to 225. I think it's a risky proposition, even though I did say it may well work. As with the adapter: Just because an arrangement appears to work initially doesn't mean it was ever really a good idea.
By the way, I'm also pretty sure the 12v power limit on SATA connectors is around 55W - and that's about 30% less than the
6-pin PCIe connector can provide, never mind that it's about
65% less than the 8-pin connector you're plugging it up to.
Again, will it work? It might, at least initially. Good idea? Well...not according to everything electronics and the specs say, no. I wouldn't recommend it because I wouldn't want someone to run into problems down the road.
Keep in mind it's also the original PSU , which has been around a while (admittedly, I'm assuming here). Using an older PSU to drive that much more of a load than it's ever had to, when it's already dated...well...if you say so. Not the best idea I've heard in the 35 years I've been in electronics.
And don't forget the heat constraints. If a card uses more power (as evidenced by the 8-pin connector), then it will generate more heat, probably worsening the potential for cooling problems.
Finally, as for cost - obviously, you've never been in a situation where even a few dollars makes all the difference. I indicated above that there are several models of 1060 cheaper than 1660s on NewEgg currently, so if budget matters (and it always does) then a few dollars more might be prohibitive for some people. Even when you know a few more dollars could buy you much more performance...if you can't afford it, you can't. It's very presumptuous to say something is "pointless" when you don't know someone else's situation.
(EDIT: I looked on NewEgg just now, and the least expensive 1050Ti was $160, while the least expensive 1660 was $220. So, it's actually $60 more - which is another 37.5%. May not seem like much, but if you're already strapped to come off the $160, the 1050s are great cards and this is widely known. No one's questioning that 1660s are better cards, but cost is cost.) As I mentioned, it will depend where and when you shop.
