这台旧的比特币挖矿设备又有盈利了吗？

Btc price moved a lot recently and brought back those miners that were previously disconnected. When the Btc price collapsed in March many older miners switched off their equipment. Mining bitcoin may still make sense and be profitable for some people. Whether it is still profitable depends on what equipment your friend has and how much electricity costs. The Antminer S9 hardware seems to be back in mining. Use the online profitability calculator to do a cost-benefit analysis. https://www.buybitcoinworldwide.com/mining/calculator/

This is what needs to be taken to account when both bitcoin prices and mining difficulty decrease, it usually means fewer miners and greater ease of receiving bitcoins. When bitcoin prices and mining difficulty increase, expect the opposite then more miners will compete for less bitcoins.

It all depends on the price. At this point, it may be worth it. It also depends on how old your mining equipment is. 

In my opinion, you should be interested in Ethereum mining. ETH is mined using graphics cards, which are not like ASICs and are also used for other purposes than digging.

Ideally you should use some kind of profitability calculator e.g. whattomine.com

Personally, I believe it could be worth trying to use the Antminer s9 again, especially now that the price of bitcoin has significantly increased. With the recent surge in the value of bitcoin, it is possible that the old mining equipment could become profitable once more. However, it is important to consider factors such as electricity costs and overall maintenance of the equipment before making a decision.