A quick tutorial
In simple steps using Dogecoin and the service of Blocktrades

Image cc-by-sa @oaldamster.
Let's get some
Steem Power helps you raise your voting strength. It is an investment in Steem {STM} for a longer term. For this you get a small percentage of dividend too. The value of Steem Power {SP} is the same as that of Steem. Moving your Steem Power investment back into Steem takes 13 weeks, that is called Powering Down {PD}. In this post I'm going to focus on how to buy Steem Power, the easy way.

Buy Steem or Steem Power
The most simple way to go about this is to use your build in Wallet at SteemIt dot com, for instance. There you will find a button that says: [BUY STEEM OR STEEM POWER] After you clicked on it you will be taken to the website of Blocktrades dot US. This is a fast conversion service that is very well intregrated with the Steem Social Media Platform.

Make your choice
Then you have the choice what Crypto to buy the Steem Power with. Most of the time I do use Dogecoin for this. Because it is fast and cheap to do so. You can choose which one with the 'Send...' dropdown menu, this one defaults to Bitcoin. Under 'Receive...' choose Steem Power from the dropdown menu, as this defaults to Steem.

Convert Dogecoin to Steem Power, for instance
Then fill in the amount of Steem Power you want to Receive or the amount of Dogecoin you want to send. (You could also set a Steem Wallet memo if you like.) The interface will calculate the right value for the conversion. This is however an approximation, as the Cryptos market does fluctuate.
After that you can click on the [Get Deposit Address] button, if you are sure you have all the settings set the way you want it too.

How much to covert?
The specific data then will be shown where to send the payment to, with Dogecoin and other Cryptos that will be an address. When you have a mobile it is easy to use the QR-code to make the payment. Multiwallets like CoinOmi (Android only) and JAXX (iPhone & Android) do support this.
NOTE: For Bitshares payments there will also be a Memo presented that you need to use.

Then something like this will show up
After you send the amount of Crypto, Dogecoin for instance, Blocktrades will wait for it to arrive. As its service is very fast it will only take a short while, at least when using DOGE that is. (Bitcoin and Ethereum might take longer and are more expensive. BTC even very expensive.) Dogecoin is the most effective way to trade for Steem and the other way round, from my own personal experience.

Very fast confirmation, and there the SP is
This 'howto' was aimed at Steemians who are new to this subject and would like to buy more Steem Power. It creates bigger rewards for curating and from 500 SP and upwards there is a Voting Power Percentage Slider that can be used. Basicly the value of Steem Power in an account Wallet determines the amount of interaction that is possible with the Steem blockchain.
Or to simplefy it even more: the more SP, the better...
Have a great one!
All screenshots were taken and edited by @oaldamster.
This is an adjusted republication of a previous outdated post about buying SP.